Erratic Mutation

Removal stapled to a slot machine, except you pull the lever after you've already committed the target. The +X/-X swing lands at instant speed and wants to be a clean kill, but the size of it is whatever the top of your library hands you: a cheap nonland is a feeble +1/-1 that barely scratches anything real, while a fat spell shrinks a creature by five or six and ends it. That variance is the whole bargain. A library leaning on high-cost spells turns this into reliable removal that dodges the dead-card problem, since revealed cards go to the bottom rather than the graveyard and nothing is burned. A library full of cheap spells makes it a gamble you cannot afford to point at a real threat. The sequencing is what makes it more than a coin flip and more than a buff: you name the creature before anything is revealed, so pointing this at your own attacker is genuinely dangerous, because a big reveal is exactly the outcome that drops its toughness through the floor and kills it. It belongs to the small family of blue effects that treat the top of the library as an interactive resource, paying for blue's traditional reluctance to kill creatures by routing the answer through information you do not yet control. The card and the mana-value distribution you build beneath it are inseparable, which collapses the deckbuilding decision and the spell into a single choice.