Urborg Skeleton

Regenerating skeletons are one of black's oldest defensive idioms, going back to Drudge Skeletons in Alpha, and this is the Invasion-block answer to the same brief: a body that refuses to die in combat for a mana you were going to leave open anyway. What sets it apart from its forebears is the kicker clause grafted on top. Early in the game it costs a single black and walls a creature indefinitely, blocking and regenerating turn after turn while you do other things. Later, when that mana stops mattering, the same card draws a second use: pay the extra three and it shows up as a 1/2 instead of a 0/1, trading a chump-blocker for a body that can actually trade. The design is purely about smoothing the curve. The first copy you draw is a one-drop you want; the fourth copy you draw in the late game is not dead weight, because the kicker gives the redundant mana somewhere to go. It is a small, honest piece of the kicker philosophy that defined its set: every card should have a floor that works on turn one and a ceiling that works on turn ten, with no separate card needed to bridge them.