Cheapest priced copy (The List): $0.35 at Card Kingdom, near mint, their price list as of .
Warriors' Lesson 
Instant · Uncommon · Theros · #184
Until end of turn, up to two target creatures you control each gain "Whenever this creature deals combat damage to a player, draw a card."
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper