Coral Net

Coral Net sees essentially no competitive play anywhere it's legal. In Commander, the condition — destroying a creature when its controller taps a non-blue land — is too unreliable against most four- and five-color decks where the trigger fires constantly, but those same decks run enough redundancy that losing one creature barely matters, and against mono-blue it does nothing at all. Legacy and Vintage have access to interactive cards that answer threats immediately and unconditionally; Coral Net's sorcery-speed-adjacent dependency on the opponent's land choices puts it below the threshold. Pauper is the one format where hyper-specific enchantment-based hate occasionally carves a niche, but even there, the green and red aggro decks it might target would rather see you spend that slot on something proactive.