In Magic: The Gathering, an early-round mana boost can be game-changing, and Mana Vault is one of the most cost-effective ways to achieve this, especially if it's played alongside cards with an untap effect
Transforming Kuja grants a damage-doubling effect, a Commander favorite
The Demons Mirror Monster borderless variant is its most expensive
The thing I really don't like about Morbid OpportunistMorbid Opportunist, though, is that it fails to do the most important thing for a creature deck: Help you recover or even punish a board wipe
As that ability resolves, if the creature has a +1/+1 counter on it for any reason, you simply won't put any +1/+1 counters on it
FlashbackTap three untapped white creatures you control