SC2Mapster

Look at how the overlord and zergling do it. Most land Zerg units also do it for burrowing.

You need the following.

• Morph class ability. This is used to setup the morph relationship for the unit. Add it to your "mutalisk". Several examples are included in the game (recommend seeing Corruptor->Broodlord and Overlord->Overseer as they closely match what you want to do).
• A button for the morph. You can base it on the morph button for Broodlord or Overseer as they will have the appropriate tooltip format for use as a template.
• A command card entry in the "mutalisk" unit type of type ability order that uses the button and issues the morph order. Make sure Mutalisk has the morph ability as part of its ability list as otherwise the order cannot be linked to the button.
• A requirement for when the morph is allowed to occur. This is added to the Morph ability under the specific morph entry in the appropriate morph requirement field. See Broodlord or Overlord morph for a good example of a requirement for a specific building and where the requirement is entered.
• An unit type for your "guardian". This can be based on other Zerg air units just as a template. Modify its stats to be what you desire. Add it to the morph ability at the appropriate morph entry. Cost for morph is defined here and do remember that by default it is resource conservative (so the amount you pay is the resulting morph unit type minus the base morph unit type, even refunding when appropriate).
• An unit type actor for your "guardian". This should be based on either the overseer or broodlord and will probably be the hardest thing to get right. You will need to change all actor event references to match your new unit and ability data and not the old units. Delete actor events that are not appropriate (eg abilities that it will not possess). To get the cocoon animation you would want to carefully examine all actors involved and duplicate them while updating references. This is not easy, you need to make sure all the referred unit types in the events make sense as during duplication most will probably link to the wrong data entries. If something looks wrong about your Guardian the problem will be actor related.