Giant Koi

In Commander, Giant Koi fits blue-green tempo and sea-creature tribal shells where a two-mana 6/6 creates immediate board pressure and threatens to end games fast in a multiplayer context. The drawback is more punishing at a four-player table where any opponent can cash it in, so you want ways to protect it or turn the drawback into an upside — bounce effects, sacrifice outlets, or flicker loops all work. In competitive 1v1 formats like Legacy and Modern, a 6/6 for UG is statistically efficient, but the opponent having a free "destroy this" attached to a basic land drop makes it unreliable as a threat in serious builds. Pauper is where Giant Koi is at its most interesting outside Commander, since 6/6s at common are genuinely unusual and tempo decks can occasionally race around the downside.