Blood Frenzy

A pump spell that bills you on the back end: the +4/+0 lands a kill or trades up in combat, and then the next end step collects, destroying the creature you just empowered if it is still around. That self-immolating destroy clause is what prices the swing. The card reads as a beating in the red deck's favor, but the restrictions (cast only before the combat damage step, and only on a creature already committed to attack or block) are the rest of the cost. You cannot hold up a midcombat trick at any time; you have to commit the spell into a creature that is locked into the combat math, then accept that you are spending the creature too. The most common honest use is firing it at your own attacker to push four extra damage through, then letting it die having served its purpose, which is functionally a burn spell stapled to a body's last swing. The other line ignores the pump entirely: aim it at an enemy attacker or blocker purely for the end-step destroy, treating the +4/+0 as a tax you have to survive (you would rather not be handing an opponent's creature four power) in exchange for likely removal of something already pinned in combat. Tempest treated the combat step as its own resource, and Blood Frenzy reads the attacking-or-blocking declaration as the cost of admission: the creature is already spent the moment it taps, so the card just asks you to spend it harder.