Lord Shivshankar obtained a boon by propitiating Lord Shree Ganesh who stays at Manipur,
who gave boon to Mahadev, whose appearance is beautiful & pleasing & who is statue of good qualities.
 

Mahaganapati means powerful Ganapati. Mahaganapati has eight, ten or twelve hands.Lord Shivshankar got victory over Tripurasur (demon) on worshipping Mahaganapati. Therefore it is called "tripurari Varado Mahaganapati.
(Lord Shivshankar is called as Tripurari after his victory over Tripurasur)