The Squadron Sinister is a rare Legendary Creature — Human Villain card from Marvel Super Heroes Commander (MSC), collector number 417. Current market price: $2.05, TCGplayer market prices via Scryfall.
Flying, haste Other Villains you control get +2/+2 and have flying and haste. Mayhem {3}{U}{R} (You may cast this card from your graveyard for {3}{U}{R} if you discarded it this turn. Timing rules still apply.)