Since you can do this at instant speed, dumping mana into Gretchen Titchwillow just before your last opponents end of turn is a great way to maximize your resources while keeping everything open for a well-timed counterspell
Summon: Bahamut Yes, its 9 mana, but its one of the best colorless cards to cheat into play
Finally, Cube is a limited format like Draft except the packs are from a curated collection of cards rather than simply cracking random set packs
With a reasonable mana value, triggered creature-token creation, and land ramp, this Sultai commander is a prime choice to lead a graveyard recursion deck
It remains to be seen, however, how GameStops entry into the secondary card marketplace will impact independent retailers