Thorn Lieutenant is a rare Creature — Elf Warrior card from Core Set 2019 Promos (PM19), collector number 203p. Current market price: $0.44 (foil $1.36), TCGplayer market prices via Scryfall.
Whenever this creature becomes the target of a spell or ability an opponent controls, create a 1/1 green Elf Warrior creature token. {5}{G}: This creature gets +4/+4 until end of turn.