Skittering Crustacean is a common Creature — Crab card from Conspiracy: Take the Crown (CN2), collector number 36. Current market price: $0.29 (foil $0.42), 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.)