If Jenova dies at the same time as one or more Mutants you control, its last ability will trigger for each of those Mutants (including itself if it somehow became a mutant)
There is no such thing as overkill because nearly every deck is just trying to goldfish into the most efficient ways to win
Alternatively, if you want to keep things at a more wholesome level, you could decide to just keep Reaper King waiting in the Command Zone, looming over the game and bringing terror without ever even being cast.
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Theater of Horrors The Adventures in the Forgotten Realms precon led by Prosper, Tome-Bound is one of the most fun precons Ive played
Obviously, there are some silly things you can do with utility lands, and the potential alone has people pumping the preorder price up here