Wizkids Rules!

When played, does the possession die itself take control of the opposing die, or must one of your characters act as the controller?

Possession: At the start of your Attack step, take control of an opposing character with a lower level than one of your characters. Attack with it.

In this case, there is no 'controlling' die, but feel free to use the Possession die as a reminder that the effect is at play (since the die would be Out of Play anyway).

-The Dice Masters Rules Team