wow!
I'm not sure if I understood correctly...
A permanent that destroys with no cost for 2
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maintenance
I love the idea but I'm pretty sure that it's OP. Spark + Inmolation + 2 burning towers and at the very first turn you start to blow up things like crazy.
What if, instead of paying a maintenance, you have to sacrifice a permanent to destroy an opponent's permanent? The advantage is that you can choose what to sacrifice and destroy, of course. And also you can choose to sacrifice Magma.
Hope you like the idea.