Goblin Fire Fiend

A must-be-blocked clause stapled to a 1/1 looks like a misprint until you notice what it deletes from the opponent's decision tree. "This creature must be blocked if able" doesn't hand you the matchup: the defender still picks which creature blocks. What it removes is the option to let four mana's worth of Goblin sail in for nothing. That deleted refusal is the entire engine. Someone has to commit a blocker, which means tying up a body that wanted to attack, walking a creature into your combat trick or a deathtouch body waiting in the wings, or eating the trade just to stop a clock the 1/1 was never going to deliver on its own. The firebreathing line is the consolation prize, the reason the card isn't a pure embarrassment in topdeck mode, but it's cover, not the point. Forced-block effects are red's way of turning the defensive step into an obligation rather than a choice, a puzzle the opponent is contractually required to solve: who blocks, what they spend doing it, what else gets through while they're occupied. Haste means the demand lands the turn it arrives rather than telegraphing for a cycle. The body's fragility never gets rescued, and that's the bargain in full: the card spends its own life expectancy to make an opponent spend something on a creature they'd have happily ignored, and being ignorable is precisely what it refuses to allow.