Designed the basic blocks in the extension

levels.ts

@@ -0,0 +1,34 @@
+//% color=#20bf6b weight=100 icon="\uf0ae"
+namespace levels {
+
+    /**
+    Change the current level that is playing
+    **/
+    //% block
+    //% l.defl=1
+    export function startLevel(l: number = 1) {
+    }
+
+    /**
+    Restart the current level
+    **/
+    //% block
+    export function restartLevel() {
+    }
+
+    /**
+    Start the next level (increment level by one)
+    **/
+    //% block
+    export function startNextLevel() {
+    }
+
+    /**
+    Set the code to run on the start of each level
+    @param l the level number
+    **/
+    //% block="on start level $l"
+    //% l.defl=1
+    export function onStartLevel(l: number = 1, handler: () => void): void {
+    }
+}

main.blocks

@@ -1 +1 @@
-<xml xmlns="https://developers.google.com/blockly/xml"><variables><variable id="N?FY*G*IS#wMe%RQ)SQr">value</variable><variable id="ZF;V,?GK~M=;bIAH$8CJ">list</variable></variables><block type="pxt-on-start" id="8nuM@-?-?%%;/r/|yHC?" x="0" y="0"></block></xml>
+<xml xmlns="https://developers.google.com/blockly/xml"><block type="pxt-on-start" id="@!{Ymfd?WLn82.Z50V$L" x="0" y="0"></block></xml>

pxt.json

@@ -8,7 +8,8 @@
         "main.blocks",
         "main.ts",
         "README.md",
-        "assets.json"
+        "assets.json",
+        "levels.ts"
     ],
     "testFiles": [
         "test.ts"
@@ -20,5 +21,5 @@
     "supportedTargets": [
         "arcade"
     ],
-    "preferredEditor": "blocksprj"
+    "preferredEditor": "tsprj"
 }