If X is 5 or more, destroy all other creatures
It makes sense, then, that our first card on this list is one that costs two blue and one black to cast: Undermine
I knew that as soon as I saw it, I was talking with my friend, fellow red-lover Ronny Serio, about how insane the card was
Whenever another creature you control with base power 1 enters, it gains haste until end of turn
When you consider that any deck wanting to pull this off will likely have plenty of ways to ensure it happensfrom proliferation, to protection, to being able to activate loyalty abilities more than once a turnits easy to see how this thing can do serious work in Commander
Off the top of my head this card slots into Raise the Past decks, as you can flip Sephirtoh pretty easily with Bartolome del Presidio and fodder like Nesting Bot and Infestation Sage