when did japanese pokemon cards change back vs English Pokémon Cards: Trade Value, Rarity, and Collector – Ravaver Touch Generation Change! Old Back

These cards may be played as though mechanically identical to their non-misprint counterparts to correctly match double-faced cards based on the front face of the card and do not represent mechanically unique printings

Dog Umbra

Weakness / Resistance / Retreat Cost: Gx2 / None / 2

Theres also the matter of investment, since players with bigger budgets naturally have more cards to choose from which can create a huge gap between players

Marvo would be a great commander for a deck manipulation strategy to get big-mana spells cast after winning clashes, but you're better off making a fresh deck that better supports this strategy