Madness is a Spell.
How to Get Edit
Alternatively, it can be used to remove a troublesome blocker, and then attack with it as well.
If you transform a unit after you steal it, with a card like Unstable Form, you do not keep the transformed unit. It will return to your opponent at the end of turn.
Cards you steal that die while under your control will go to your void. If the card is returned to play, it will remain under your control, even if it is returned on the same turn it is stolen.
If you have a full board when you take control of a unit, the unit will go directly to your void.