Giving your entire board +1/+1 isnt the most impressive payoff in the world just look at the middling inclusion rate of Goldnight Commander if you dont believe me but he makes up for that by generating energy counters himself as long as youve got Metalcraft set up, which is effectively free these days with all the investigating, spelunking, and cooking Wizards keeps forcing me to do against my will
Its equip cost is pricey at three mana, but once its granting +5/+5 or more, that wont seem like a lot
Beyond just being rare, thanks in part to the limited-run printing of Secret Lair drops, and their Bonus Cards, Mana Vault is insanely strong
(As they enter the field in the ready position.) Each card - both the challenger and the card being challenged - then deal damage to each other, equal to their strength value
Modern Treasure makers and white's catch-up effects provide enough mana development to support aggressive and equipment-focused Commander strategies