River Boa

In Commander, River Boa is a role-player rather than a headliner — islandwalk becomes effectively unblockable the moment any opponent is running blue, which is common enough to make the clause genuinely threatening rather than situational. Regenerate is less flashy than indestructible but it stacks well against attrition, especially in longer games where wrath effects fly every few turns. In Pauper, the card has real teeth — two mana for a renewable threat with evasion is legitimate in a format where resources are thin. Legacy and Vintage won't touch it; the bar there is simply too high for a vanilla-sized body. Overall, Commander and Pauper are the only formats where River Boa is doing meaningful work.