Cheapest priced copy (Tarkir: Dragonstorm): $0.49 at Card Kingdom, near mint, their price list as of .
Kotis, the Fangkeeper 
Legendary Creature — Zombie Warrior · 2/1 · Rare · Tarkir: Dragonstorm · #202
Indestructible
Whenever Kotis deals combat damage to a player, exile the top X cards of their library, where X is the amount of damage dealt. You may cast any number of spells with mana value X or less from among them without paying their mana costs.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
4 printings · $0.49 to $4.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Tarkir: Dragonstorm Promos | 202p | Rare | $0.59 | $0.99 |
| Tarkir: Dragonstorm Promos | 202s | Rare | — | $4.99 |
| Tarkir: Dragonstorm | 202 | Rare | $0.49 | $0.79 |
| Tarkir: Dragonstorm | 362 | Rare | $0.49 | $2.99 |
4 rulings from Wizards of the Coast
- 4 April 2025You cast the spells from among the exiled cards while Kotis’s last ability is resolving and still on the stack. You can’t wait to cast them later in the turn. Timing restrictions based on the card’s type are ignored.
- 4 April 2025If any of the spells you cast has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 4 April 2025Since you are using an alternative cost to cast the spells, you can’t pay any other alternative costs. You can, however, pay additional costs, such as kicker costs. If the spells have any mandatory additional costs, you must pay those.
- 4 April 2025If an exiled card has {X} in its mana cost, X is 0 for the purpose of determining its mana value.