Here is the scene where Goku re-appears and helps out G-Merl and the other heroes fight the black arms in G-Merl's Eternal Quest.
(As the Black Arms go down, more comes forward to use they're guns at them)
Donkey Kong: Whoa, they've got gun's, look out!!
Yoshi: Yow....! we gotta get....! out of....! the way?!!
(G-Merl and the others runs off but then they come across a dead end)
Yoshi: We're trapped!
(Then the Black arms arrive and ready to shoot the heroes)
???: Take cover!
(Then a powerful beam came out of nowhere blasting the black arms away, then a shadowy figure appears landing on the ground)
G-Merl: Who are you?
(Then, the shadowy figure turn's out to be Goku)
Goku: G-Merl, it's me, Goku.
Emerl: What a perfect time to help us out.