Stoic Sphinx

A 5/3 flyer at four mana is the shape Wizards reaches for when it wants a beater that outruns removal but dies to the same removal it outruns: three toughness folds to almost any burn spell, and a body like this normally trades or dies on schedule. The hexproof clause rewrites that math, but on a condition that cuts directly against how a blue deck wants to spend its turns. The shield holds only as long as you have not cast a spell that turn, which means the very act of firing off an instant on the opponent's turn (the thing counter-and-removal decks are built to do) drops the protection and opens a window for an instant-speed answer. Flash sharpens the tension rather than resolving it: deploying this on the opponent's turn is itself casting a spell, so it enters unprotected for the rest of that turn; the hexproof only comes back on a turn where you have not yet cast a spell. The discipline the card demands is sequencing your interaction so the turns you tap out for spells are not the turns you need this creature to survive. Hold your mana across a clean turn and the fragile body stops mattering; reach for one reactive spell too many, or drop the Sphinx into an open board mid-combat, and you hand the opponent the exact opening the toughness always left there.