At time of writing, there are only two known commons that reward this unnamed mechanic: Arena Trickster, which turns from an unexciting Hill Giant into a Rampaging Baloth (and can continue to grow), and Naiad of Hidden Coves, which allows you to play two Vexing Gulls on turn four
B+ Nightveil Specter At three mana, Nightveil Specter provides an exciting cipher target and comes with creative milling built in
Terra Branford - Urza, Lord High Artificer (Showcase) from Universes Beyond: FINAL FANTASY: Through the Ages Details Terra Branford - Urza, Lord High Artificer (Showcase) is a Mythic Rare in the set Universes Beyond: FINAL FANTASY: Through the Ages.
You almost never play it until youre ready to go off and when you do, you win on the spot, usually
In all seriousness, Mmmenon is a very exciting prospect for Commander
To be clear, Tinybones, the Pickpocket is no Ragavan, but its got similarities