The Mindskinner {U}{U}{U}
Legendary Enchantment Creature — Nightmare
BlueCommander: legal
Identity
Blue
EDHREC rank
#2,172
Cheapest printing
US$3.03
TCGplayer
Printings
4
The Mindskinner can't be blocked.
If a source you control would deal damage to an opponent, prevent that damage and each opponent mills that many cards.
Keywords: mill
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.