When it consumes the aptly named rare earth mineral Steelixite, a steelix will transform into a mega steelix. A mega steelix’s size increases to Huge, its ac increases to 23, its attack modifier increases to +9, its saving throw DCs increase to 17, its damage vulnerabilities become resistances , it gains a flying speed of 30 feet, can make one additional iron head attack as part of its multiattack action, and gains the following features: Legendary Resistance (3/Day).