Emrakul as the ultimate trump and combo piece, then 10 signet's. After that I want Aether vial, isochron scepter, and Brain in a Jar, a few stand out "options" cards like lithoform engine, staff of dominion, oblivion stone, primal amulet, and the rest low CMC filtering/CA artifacts that enable concsistency and mana outlets but diminish over time. I like the effect of scroll rack, top, crystal ball, and pendant on enabling combo's and interaction, but don't want the play pattern where this is occurring like all the time. Additionally, a few of the more limited ones I put in can be "reset" by blinking, giving an astute flicker play the ability to gain CA. Many decks should be able to pick up a piece for good use regardless, but can be built around as well. Many of these aid in double spelling in a single turn, which is another key aspect of a stack based cube. Who can cast two spells first? I'm a little torn now because after an initial lockdown of the ideal 25, I think I do want lifecrafter's bestiary. It offers what the creature heavy decks need, a way to turn their more proactive creatures into 2 for 1 and it passively increases consistency.

Whoops, I forgot colorless spells and creatures! This may mean a rework. Scour from existence, elder deep-fiend, ancient stone idol, darksteel sentinel, and hollow one definitely merit consideration.