Plain Walker is a rare Creature — Kithkin Rogue card from Mystery Booster 2 (MB2), collector number 522. Current market price: $0.22, TCGplayer market prices via Scryfall.
Plainswalk Planeswalkerwalk (This creature can't be blocked as long as defending player controls a planeswalker.) Whenever Plain Walker deals combat damage to a player or planeswalker, planeswalk. (If you're playing Planechase, proceed to the next plane.)