What would happen if you suddenly turned into what your avatar was?

[Subach]

If I turned into the symbol of Tzeentch, I guess I'd be used to summon Screamers and other awesome Tzeentchian demons.

If I was turned into a servant of Tzeentch, it'd depend on what kind.

If I was a thrall wizard, I'd probably get to think "Oh shi-" before my very essence is sacrificed to power a Chaos space marine sorcerer of Tzeentch.
If I was turned into a Tzeentch Sorcerer, I'd go around, quite literally raining hell itself on my enemies while a squad of loyal automatons followed me around, shooting anything that moves.

It'd be the life.