Mighty Mask is one of the finalists in the 25th World Martial Arts Tournament. Apparently, Mighty Mask did not fare well in the previous World Martial Arts
Tournament. He never gets to fight in the competition as he is knocked out by Trunks before the tournament begins. Trunks and Goten then steal his costume and fight in the tournament as Mighty Mask until Android 18 exposes them.
Mighty Mask is only shown in Dragon Ball Z. He is not seen after the Budokai Tenkaichi tournament
He was Killed By Buu Either during the Human genocide
attack, or the destruction of the earth. It is likely he was wished back with everyone else.