Mm'menon, the Right Hand {3}{U}{U}
Legendary Creature — Jellyfish Advisor
BlueCommander: legal
Identity
Blue
EDHREC rank
#4,886
Cheapest printing
US$0.33
TCGplayer
Printings
4
Flying
You may look at the top card of your library any time.
You may cast artifact spells from the top of your library.
Artifacts you control have "{T}: Add {U}. Spend this mana only to cast a spell from anywhere other than your hand."
Keywords: flying
Every printing
highest TCGplayer market first; a card with only a thin single listing shows its low
In short
A Commander deck is a commander and 99 other cards, one copy of each (except basic lands), all inside the commander's colour identity. Paste a full list into the deck price calculator to price it and check it against the format.