3 jet engines to coincide with the card's name. The card's info says: BTTR-EN039: Mach 3 Continuous Spell Once per turn: You can target 1 Pony or 25th Pony-Type monster with 3000 ATK or DEF; its ATK becomes 5000, until the end of this turn, but send all cards in your hand to the Grave. (Common)
