Zellix, Sanity Flayer {2}{U}
Legendary Creature — Horror
BlueCommander: legal
Identity
Blue
EDHREC rank
#3,040
Cheapest printing
US$24.40
TCGplayer
Printings
2
Hive Mind — Whenever a player mills one or more creature cards, you create a 1/1 black Horror creature token.
{1}, {T}: Target player mills three cards.
Choose a Background (You can have a Background as a second commander.)
Keywords: choose a background, hive mind, 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.