Unnatural Endurance

Two effects sharing one card, neither of which usually wants to fire at the same moment. The +2/+0 wins a combat trade you'd otherwise lose; the regenerate fizzles a removal spell or shrugs off a chump blocker's worth of damage. Bundling them onto a single one-mana instant means you almost always pay for one mode and get the other as garnish, which is the honest cost of a flexible trick: it is rarely the best version of either thing. The colorlessness stapled onto a black instant is the real curiosity. It exists to feed the cost-reduction and color-matters mechanics built around colorless spells and permanents of that era, but on the card itself it changes nothing about what the trick does or who casts it, since you still need a black source to play it. That gap (a black-pip combat trick the rules insist is colorless) is the closest thing to a hook here, and it is a hook about a design experiment rather than about the effect. As pump-and-protect, this sits in a long line of one-mana black tricks; what separates it is the bookkeeping wrinkle stamped on top, not the gameplay underneath.