Explosive Singularity 8RR
Sorcery (Mythic Rare)
As an additional cost to cast this spell, you can tap any number of untapped creatures you control. This spell costs 1 less for each creature tapped this way.
Explosive Singularity deals 10 damage to any target.
Convoke seems like a good way to power a spirit bomb, don't you think? Hidetsugu seems to think so.