diff --git a/src/engine/runtime.js b/src/engine/runtime.js
index c2e37f3c..f26d7cdb 100644
--- a/src/engine/runtime.js
+++ b/src/engine/runtime.js
@@ -123,16 +123,6 @@ const cloudDataManager = () => {
     };
 };
 
-/**
- * Predefined "Converted block info" for a separator between blocks in a block category
- * @type {ConvertedBlockInfo}
- */
-const ConvertedSeparator = {
-    info: {},
-    json: null,
-    xml: '<sep gap="36"/>'
-};
-
 /**
  * Numeric ID for Runtime._step in Profiler instances.
  * @type {number}
@@ -866,22 +856,20 @@ class Runtime extends EventEmitter {
         }
 
         for (const blockInfo of extensionInfo.blocks) {
-            if (blockInfo === '---') {
-                categoryInfo.blocks.push(ConvertedSeparator);
-                continue;
-            }
             try {
                 const convertedBlock = this._convertForScratchBlocks(blockInfo, categoryInfo);
-                const opcode = convertedBlock.json.type;
                 categoryInfo.blocks.push(convertedBlock);
-                if (blockInfo.blockType !== BlockType.EVENT) {
-                    this._primitives[opcode] = convertedBlock.info.func;
-                }
-                if (blockInfo.blockType === BlockType.EVENT || blockInfo.blockType === BlockType.HAT) {
-                    this._hats[opcode] = {
-                        edgeActivated: blockInfo.isEdgeActivated,
-                        restartExistingThreads: blockInfo.shouldRestartExistingThreads
-                    };
+                if (convertedBlock.json) {
+                    const opcode = convertedBlock.json.type;
+                    if (blockInfo.blockType !== BlockType.EVENT) {
+                        this._primitives[opcode] = convertedBlock.info.func;
+                    }
+                    if (blockInfo.blockType === BlockType.EVENT || blockInfo.blockType === BlockType.HAT) {
+                        this._hats[opcode] = {
+                            edgeActivated: blockInfo.isEdgeActivated,
+                            restartExistingThreads: blockInfo.shouldRestartExistingThreads
+                        };
+                    }
                 }
             } catch (e) {
                 log.error('Error parsing block: ', {block: blockInfo, error: e});
@@ -986,6 +974,25 @@ class Runtime extends EventEmitter {
         };
     }
 
+    /**
+     * Convert ExtensionBlockMetadata into data ready for scratch-blocks.
+     * @param {ExtensionBlockMetadata} blockInfo - the block info to convert
+     * @param {CategoryInfo} categoryInfo - the category for this block
+     * @returns {ConvertedBlockInfo} - the converted & original block information
+     * @private
+     */
+    _convertForScratchBlocks (blockInfo, categoryInfo) {
+        if (blockInfo === '---') {
+            return this._convertSeparatorForScratchBlocks();
+        }
+
+        if (blockInfo.blockType === BlockType.BUTTON) {
+            return this._convertButtonForScratchBlocks(blockInfo);
+        }
+
+        return this._convertBlockForScratchBlocks(blockInfo, categoryInfo);
+    }
+
     /**
      * Convert ExtensionBlockMetadata into scratch-blocks JSON & XML, and generate a proxy function.
      * @param {ExtensionBlockMetadata} blockInfo - the block to convert
@@ -993,7 +1000,7 @@ class Runtime extends EventEmitter {
      * @returns {ConvertedBlockInfo} - the converted & original block information
      * @private
      */
-    _convertForScratchBlocks (blockInfo, categoryInfo) {
+    _convertBlockForScratchBlocks (blockInfo, categoryInfo) {
         const extendedOpcode = `${categoryInfo.id}_${blockInfo.opcode}`;
 
         const blockJSON = {
@@ -1135,6 +1142,43 @@ class Runtime extends EventEmitter {
         };
     }
 
+    /**
+     * Generate a separator between blocks categories or sub-categories.
+     * @param {ExtensionBlockMetadata} blockInfo - the block to convert
+     * @param {CategoryInfo} categoryInfo - the category for this block
+     * @returns {ConvertedBlockInfo} - the converted & original block information
+     * @private
+     */
+    _convertSeparatorForScratchBlocks (blockInfo) {
+        return {
+            info: blockInfo,
+            xml: '<sep gap="36"/>'
+        };
+    }
+
+    /**
+     * Convert a button for scratch-blocks. A button has no opcode but specifies a callback name in the `func` field.
+     * @param {ExtensionBlockMetadata} buttonInfo - the button to convert
+     * @property {string} func - the callback name
+     * @param {CategoryInfo} categoryInfo - the category for this button
+     * @returns {ConvertedBlockInfo} - the converted & original button information
+     * @private
+     */
+    _convertButtonForScratchBlocks (buttonInfo) {
+        // for now we only support these pre-defined callbacks handled in scratch-blocks
+        const supportedCallbackKeys = ['CREATE_LIST', 'CREATE_PROCEDURE', 'CREATE_VARIABLE'];
+        if (supportedCallbackKeys.indexOf(buttonInfo.func) < 0) {
+            log.error(`Custom button callbacks not supported yet: ${buttonInfo.func}`);
+        }
+
+        const extensionMessageContext = this.makeMessageContextForTarget();
+        const buttonText = maybeFormatMessage(buttonInfo.text, extensionMessageContext);
+        return {
+            info: buttonInfo,
+            xml: `<button text="${buttonText}" callbackKey="${buttonInfo.func}"></button>`
+        };
+    }
+
     /**
      * Helper for _convertForScratchBlocks which handles linearization of argument placeholders. Called as a callback
      * from string#replace. In addition to the return value the JSON and XML items in the context will be filled.
diff --git a/src/extension-support/block-type.js b/src/extension-support/block-type.js
index 3b38c051..e7f0b18d 100644
--- a/src/extension-support/block-type.js
+++ b/src/extension-support/block-type.js
@@ -8,6 +8,11 @@ const BlockType = {
      */
     BOOLEAN: 'Boolean',
 
+    /**
+     * A button (not an actual block) for some special action, like making a variable
+     */
+    BUTTON: 'button',
+
     /**
      * Command block
      */
diff --git a/src/extension-support/extension-manager.js b/src/extension-support/extension-manager.js
index 99fa83bf..30bc6d50 100644
--- a/src/extension-support/extension-manager.js
+++ b/src/extension-support/extension-manager.js
@@ -375,16 +375,24 @@ class ExtensionManager {
             blockAllThreads: false,
             arguments: {}
         }, blockInfo);
-        blockInfo.opcode = this._sanitizeID(blockInfo.opcode);
+        blockInfo.opcode = blockInfo.opcode && this._sanitizeID(blockInfo.opcode);
         blockInfo.text = blockInfo.text || blockInfo.opcode;
 
-        if (blockInfo.blockType !== BlockType.EVENT) {
+        switch (blockInfo.blockType) {
+        case BlockType.EVENT:
+            if (blockInfo.func) {
+                log.warn(`Ignoring function "${blockInfo.func}" for event block ${blockInfo.opcode}`);
+            }
+            break;
+        case BlockType.BUTTON:
+            if (blockInfo.opcode) {
+                log.warn(`Ignoring opcode "${blockInfo.opcode}" for button with text: ${blockInfo.text}`);
+            }
+            break;
+        default:
             blockInfo.func = blockInfo.func ? this._sanitizeID(blockInfo.func) : blockInfo.opcode;
 
-            /**
-             * This is only here because the VM performs poorly when blocks return promises.
-             * @TODO make it possible for the VM to resolve a promise and continue during the same Scratch "tick"
-             */
+            // Avoid promise overhead if possible
             if (dispatch._isRemoteService(serviceName)) {
                 blockInfo.func = dispatch.call.bind(dispatch, serviceName, blockInfo.func);
             } else {
@@ -392,12 +400,11 @@ class ExtensionManager {
                 const func = serviceObject[blockInfo.func];
                 if (func) {
                     blockInfo.func = func.bind(serviceObject);
-                } else if (blockInfo.blockType !== BlockType.EVENT) {
+                } else {
                     throw new Error(`Could not find extension block function called ${blockInfo.func}`);
                 }
             }
-        } else if (blockInfo.func) {
-            log.warn(`Ignoring function "${blockInfo.func}" for event block ${blockInfo.opcode}`);
+            break;
         }
 
         return blockInfo;