Serpent-Blade Assailant is a common Creature — Elf Warrior card from March of the Machine (MOM), collector number 205. Current market price: $0.24 (foil $0.18), TCGplayer market prices via Scryfall.
Backup 1 (When this creature enters, put a +1/+1 counter on target creature. If that's another creature, it gains the following ability until end of turn.) Deathtouch