Skittering Crustacean is a common Creature — Crab card from The List (PLST), collector number CN2-36. Current market price: $0.36, TCGplayer market prices via Scryfall.
{6}{U}: Monstrosity 4. (If this creature isn't monstrous, put four +1/+1 counters on it and it becomes monstrous.) As long as this creature is monstrous, it has hexproof. (It can't be the target of spells or abilities your opponents control.)