those are the "chaos" abilitys, which change the type of a unit from one to another. bonuses from auras, items, ext all become perminent after such a transformation.
I would just avoid avatar entirely and go with chemical rage, its a safe morph ability. Don't use metamorphosis because its hardcoded to give the unit a missile attack.
Avatar can also lead to control loss bugs that can only be fixed by destroying and recreating the unit.
Metamorphosis isn't hardcoded to give a ranged attack, it just happens to be that the other form has a ranged attack AND a melee attack, yet only the ranged attack is allowed.
You can use virtually any (not Chaos) morph ability that you want provided you know how to use the flags and manipulate it properly. Chemical Rage is a good one as you do not have to change tooooooooooo much.
avatar basically just gives you spell immune and bonus life, dmg... what i did is that just code those things manually using triggers~ adding spell immunity ability, bonus life and damage and so on, and also the *growing bigger* thing can be done by using trigger :D
Control loss is a good reason to stop using morph spells altogether, i.e. Avatar, Chemical Rage, Metamorphosis, etc. So you probably want to go zen87's way, it's clearly the safest option.
