Power Attacks are Special Attacks available natively to Warjacks and Warbeasts. Monstrosities are counted as Warjacks in terms of preforming and being targeted by Power Attacks.
Warjacks and Warbeasts with two Open Fist weapon can also make the Double Hand Throw Power Attack
Warjacks and Warbeasts with a large (50 mm) or huge (120 mm) base can also make the Trample Power Attack.
Colossals & Gargantuans can make the Sweep Power Attack.
Colossals & Gargantuans with at least one Open Fist can make the Power Strike Power Attack.