Lulu, Stern Guardian {2}{U}
Legendary Creature — Human Wizard
BlueCommander: legal
Identity
Blue
EDHREC rank
#3,428
Cheapest printing
US$0.31
TCGplayer
Printings
4
Whenever an opponent attacks you, choose target creature attacking you. Put a stun counter on that creature.
{3}{U}: Proliferate. (Choose any number of permanents and/or players, then give each another counter of each kind already there.)
Keywords: proliferate
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.