Cheapest priced copy (Fallout): $0.49 at Card Kingdom, near mint, their price list as of .
Cait, Cage Brawler 
Legendary Creature — Human Warrior · 1/1 · Rare · Fallout · #409
During your turn, Cait has indestructible.
Whenever Cait attacks, you and defending player each draw a card, then discard a card. Put two +1/+1 counters on Cait if you discarded the card with the greatest mana value among those cards or tied for greatest.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
4 printings · $0.49 to $2.49 at Card Kingdom
2 rulings from Wizards of the Coast
- 8 March 2024If a card you discard has {X} in its mana cost, X is considered to be 0.
- 8 March 2024If you somehow can't discard a card (probably because you had no cards in hand and another effect prevented you from drawing cards), you won't put any counters on Cait no matter whether or not the defending player discarded a card or what that card's mana value is.