diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t01.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t01.dart
new file mode 100644
index 0000000000..e998419bbf
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t01.dart
@@ -0,0 +1,43 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it’s a compile-time error if a non-abstract class
+/// implements Enum and it is not the implicit class of an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+class C implements Enum {
+//                 ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  int get index => 42;
+}
+
+main() {
+  C? c;
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t02.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t02.dart
new file mode 100644
index 0000000000..9ad30538bc
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t02.dart
@@ -0,0 +1,49 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that abstract classes may implement enum
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+import "../../Utils/expect.dart";
+
+abstract class C implements Enum {
+  int foo();
+}
+
+enum E implements C {
+  e1,
+  e2;
+
+  int foo() => this.index;
+}
+
+main() {
+  Expect.equals(0, E.e1.foo());
+  Expect.equals(1, E.e2.foo());
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t03.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t03.dart
new file mode 100644
index 0000000000..500dd6bea4
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A01_t03.dart
@@ -0,0 +1,50 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that implicit class of enum declaration implements Enum
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+import "../../Utils/expect.dart";
+
+enum E1 {
+  e1,
+  e2
+}
+
+enum E2 {
+  e1(42),
+  e2(0);
+
+  const E2(int i);
+}
+
+main() {
+  Expect.isTrue(E1.e1 is Enum);
+  Expect.isTrue(E2.e1 is Enum);
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t01.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t01.dart
new file mode 100644
index 0000000000..b31fa02bf1
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t01.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it is a compile-time error if a class extends
+/// a class declared by an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E {
+  e1,
+  e2
+}
+
+abstract class E1 extends E {
+//                        ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class E2 extends E {
+//               ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  E1? e1;
+  E2? e2;
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t02.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t02.dart
new file mode 100644
index 0000000000..e64ca4d7a2
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t02.dart
@@ -0,0 +1,56 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it is a compile-time error if a class extends
+/// a class declared by an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E {
+  e1(42),
+  e2(0);
+
+  const E(int i);
+}
+
+abstract class E1 extends E {
+//                        ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class E2 extends E {
+//               ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  E1? e1;
+  E2? e2;
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t03.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t03.dart
new file mode 100644
index 0000000000..a1d28a50c9
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t03.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it is a compile-time error if a class implements
+/// a class declared by an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E {
+  e1,
+  e2
+}
+
+abstract class E1 implements E {
+//                           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class E2 implements E {
+//                  ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  E1? e1;
+  E2? e2;
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t04.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t04.dart
new file mode 100644
index 0000000000..3b1966723f
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t04.dart
@@ -0,0 +1,56 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it is a compile-time error if a class implements
+/// a class declared by an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E {
+  e1(42),
+  e2(0);
+
+  const E(int i);
+}
+
+abstract class E1 implements E {
+//                           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class E2 implements E {
+//                  ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  E1? e1;
+  E2? e2;
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t05.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t05.dart
new file mode 100644
index 0000000000..6e33273c18
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t05.dart
@@ -0,0 +1,59 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it is a compile-time error if a class mixes-in
+/// a class declared by an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E {
+  e1,
+  e2
+}
+
+mixin M on E {
+//         ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class C1 = Object with E;
+//                    ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class C2 extends Object with E {
+//                           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  E1? e1;
+  E2? e2;
+}
diff --git a/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t06.dart b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t06.dart
new file mode 100644
index 0000000000..332b965ef9
--- /dev/null
+++ b/LanguageFeatures/Enhanced-Enum/implementing_enum_A02_t06.dart
@@ -0,0 +1,61 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// @assertion It’s currently a compile-time error for a class to implement,
+/// extend or mix-in the Enum class.
+///
+/// Because we want to allow interfaces and mixins that are intended to be
+/// applied to enum declarations, and therefore to assume Enum to be a
+/// superclass, we loosen that restriction to:
+///
+/// It’s a compile-time error if a non-abstract class implements Enum unless it
+/// is the implicit class of an enum declaration.
+///
+/// It is a compile-time error if a class implements, extends or mixes-in a
+/// class declared by an enum declaration.
+///
+/// That allows abstract classes (interfaces) which implements Enum in order to
+/// have the int index; getter member available, and it allows mixin
+/// declarations to use Enum as an on type because mixin declarations cannot be
+/// instantiated directly.
+///
+/// This restriction still ensure enum values are the only object instances
+/// which implements Enum, while making it valid to declare abstract class
+/// MyInterface implements Enum and mixin MyMixin on Enum for interfaces and
+/// mixins intended to be used in declaring enum classes.
+///
+/// @description Check that it is a compile-time error if a class mixes-in
+/// a class declared by an enum declaration.
+/// @author sgrekhov@unipro.ru
+
+// SharedOptions=--enable-experiment=enhanced-enums
+
+enum E {
+  e1(42),
+  e2(0);
+
+  const E(int i);
+}
+
+mixin M on E {
+//         ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+class C1 = Object with E;
+//                    ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+class C2 extends Object with E {
+//                           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  E1? e1;
+  E2? e2;
+}