Cheapest priced copy (Wilds of Eldraine Promos): $9.49 at Card Kingdom, near mint, out of stock, their price list as of .
Agatha of the Vile Cauldron 
Legendary Creature — Human Warlock · 1/1 · Mythic · Wilds of Eldraine · #360
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.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
4 printings · $8.99 to $12.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Wilds of Eldraine Promos | 199p | Mythic | $9.49Out of stock | $9.99Out of stock |
| Wilds of Eldraine Promos | 199s | Mythic | — | $9.49Out of stock |
| Wilds of Eldraine | 199 | Mythic | $9.99 | $8.99 |
| Wilds of Eldraine | 360 | Mythic | $11.99Out of stock | $12.99Out of stock |
2 rulings from Wizards of the Coast
- 1 September 2023Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keyword abilities are activated abilities and will have colons in their reminder text. Triggered abilities (starting with "when," "whenever," or "at") are unaffected by the cost reduction ability of Agatha of the Vile Cauldron.
- 1 September 2023Agatha of the Vile Cauldron's first ability affects only abilities of creatures you control on the battlefield. The costs of activated abilities of creature cards that work in other zones (such as cycling) won't be reduced.