Wandering Troubadour

Wandering Troubadour is a Commander card first and foremost — the ETB value is sized for a 100-card singleton format where consistency is scarce and any scry-plus-draw on a body pulls weight. In Modern and Pioneer the rate is simply too low; a 2/2 that replaces itself doesn't pressure the board or close games in a format where three mana needs to threaten a win or halt one. Legacy and Vintage have no interest in a 3-mana do-nothing creature when those formats are over by turn two. Oathbreaker follows Commander logic closely enough that Wandering Troubadour is playable there in spell-slinger or blink shells, though the 20-card signature spell restriction compresses the deck enough that you'll often want denser engines.