Agatha of the Vile Cauldron {R}{G}
Legendary Creature — Human Warlock
Identity
Gruul
EDHREC rank
#5,674
Cheapest printing
US$4.78
TCGplayer
Printings
4
Activated abilities of creatures you control cost {X} less to activate, where X is Agatha's power. This effect can't reduce the mana in that cost to less than one mana.
{4}{R}{G}: Other creatures you control get +1/+1 and gain trample and haste until end of turn.
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.