Haunted Plate Mail

The clever bit is the failsafe built into a piece of armor: a +4/+4 Equipment is dead weight when the board is empty, so this one can stand up and walk. The animation clause turns a useless suit into a 4/4 Spirit the moment you control no other creatures, giving the card a body when nothing else survives. That conditional ("only if you control no creatures") is the whole pivot: the animation is a fallback for the wiped-out board, not a toggle you flick alongside your threats. The catch is the return trip. Once it becomes a creature it stays one until end of turn, and when it lapses back to Equipment you have to pay the full equip at sorcery speed to bolt it onto whatever finally shows up. There is no free re-attachment, no instant-speed pivot; the zero-mana animation is generous, but the four-mana equip is the real tax and it is paid on your own main phase. The result is a single card that bridges two phases of a game: a standalone clock when you have been reduced to nothing, and a heavy buff when you have not. As design it answers the old problem that haunts most Equipment (the dead card with no creature to hold it) by letting the armor be its own creature, a trick that stays rare because it asks the card to be two things at once and price both.