I like this idea, although taking over the creatures ability seems a) too powerful and b) would introduce some incosistencies. Examples: Corrupted Phoenix, is killed, turns into Ash. Does Ash use now
or
? Same with Pharao, Air Nymph? What about Passive abilities (Gemfinders, Brimstone Eaters,...)? So this has to be clarified.
Next, the quantum costs: How about changing it to 4+X
(+depletes all
), where X is the summoning cost of the target creature? This way, it adapts itself to the creature power.