Marwyn, the Nurturer

Commander is where Marwyn, the Nurturer is most at home — the 100-card singleton format's tolerance for three-mana ramp creatures is higher, the Elf tribal density in dedicated builds is deep enough to reliably trigger her counter clause multiple times per turn, and the infinite combos she enables with Staff of Domination or Umbral Mantle are viable win conditions rather than fringe interactions. In Legacy and Vintage she's legal but irrelevant; both formats move too fast for a do-nothing-on-entry creature that needs an Elf package to function, and neither format's Elf shells prioritize her over more consistent mana sources. Modern is similarly unfriendly — she competes in a format full of efficient removal at exactly the mana cost where she wants to survive a full turn cycle. Pioneer is legal but the Elf support there is thin enough that she rarely shows up outside of fringe tribal builds. Oathbreaker is the one other format where she's genuinely playable, especially as the signature spell slot enables repeated Elf-matters payoffs, and she can serve as a compact commander-equivalent in the right shell.