Here are the fusions/merging that happened in DBZ/DBGT......

-Piccolo/Nail = Piccolo
-Piccolo/Kami = Piccolo
-Trunks/Goten = Skinny Gotenks
-Trunks/Goten = Fat Gotenks
-Trunks/Goten = Gotenks
-Supreme Kai/Kabito = ?
-Goku/Vegeta = Veku/Fat Gogeta
-Goku/Vegeta = Gogeta
-Goku/Vegeta (Potera Earrings) = Vegito
-Mr.boo/Oob = Oob
-Hell Fighter No.17/No.17 = Super Android 17
-SS Goku 4/SS Vegeta 4 = SS Gogeta 4