Griselbrand [c]Griselbrand[/c] is one of the most powerful creatures in Magics history, but its steep mana cost limits the number of decks it can go into
The games I did lose were to truly abysmal draws, but the rest of the time
Kaalia of the Vast Kaalia
While this will mostly be relevant in casual play, it's worth pointing out that if you have a Naban, Dean of Iteration on the battlefield, every Wizard that enters the battlefield will trigger Warstorm Surge, Fathom Mage, Angelic Chorus, and Purphoros, God of the Forge (among others) an additional time, which opens up an entirely different layer of deck-building potential that was missing with Panharmonicon, which only triggered abilities on artifacts and creatures
Enchantment Tutor (CTRL to add secondary) Culled Chimil, the Inner Sun Spells you control can't be countered
Chase mythics in Commander-focused sets tend to hold value better than combo pieces that can be banned, making the Cosmic Cube a safer long-term hold than Bruce Banner if competitive bans become likely