Aven Riftwatcher is a common Creature — Bird Rebel Soldier card from The List (PLST), collector number PLC-1. Current market price: $0.34, TCGplayer market prices via Scryfall.
Flying Vanishing 3 (This creature enters with three time counters on it. At the beginning of your upkeep, remove a time counter from it. When the last is removed, sacrifice it.) When this creature enters or leaves the battlefield, you gain 2 life.