Ruthless Invasion

In Commander, Ruthless Invasion is a finisher in dedicated Eldrazi or devoid-tribal lists — you're not running it for incremental value, you're running it to end the game on a wide, unblockable attack. Outside of that context, five mana sorcery-speed for a one-turn buff rarely makes the cut in a format where every slot competes against reusable effects. In Pauper, the devoid synergy pool is shallow enough that Ruthless Invasion has almost no viable home. Legacy and Vintage have the raw power to end games through other means entirely, so Ruthless Invasion never sees play there. Oathbreaker follows the same logic as Commander — niche payoff in the right shell, invisible everywhere else.