Saprazzan Outrigger

A 5/5 for four mana that you can never actually keep, and the math on that trade is harsher than the body suggests. The trigger fires at end of combat, after damage is dealt and taken, so the creature behaves like a normal attacker or blocker in the moment: it deals its five, it can die to lethal damage before the trigger ever resolves, and only if it survives does it tuck itself back onto your library. That placement is the real cost. Your next draw step is spent re-drawing this creature instead of finding anything new, so each combat it survives effectively eats a turn's worth of card flow and a full recast. You are not getting a recurring threat; you are renting a 5/5 swing and paying the rent in tempo and cards. The upside is that nothing on the board can punish it between combats: it never lingers to be picked off by sorcery-speed removal, and an opponent has to deal with it during the one combat it shows up for or watch it disappear. The design instinct here is the old habit of handing out aggressive stats and then leashing them with self-bounce or self-tuck, the same impulse behind creatures you had to keep re-buying turn after turn. The leash is unusually tight: a body big enough to matter, attached to a tax you pay every single time you want it to matter again.