Arasta of the Endless Web is a rare Legendary Enchantment Creature — Spider card from Theros Beyond Death Promos (PTHB), collector number 165p. Current market price: $0.73 (foil $1.50), TCGplayer market prices via Scryfall.
Reach Whenever an opponent casts an instant or sorcery spell, create a 1/2 green Spider creature token with reach.