While in his first form, Janemba attacks Goku by punching into small portals big enough for his fists. By doing this, Janemba is able to hit Goku with a series of punches from a distance away.
Appearances in games
Illusion Smash was named in Dragon Ball Z: Budokai Tenkaichi 2 as well as the game's sequel, Dragon Ball Z: Budokai Tenkaichi 3 as Janemba's Ultimate Blast in his first form in both games. In Dragon Ball Z: Buu's Fury, Janemba uses this technique, creating enemies called Janemba Hands, to attack Goku and Vegeta while they travel through Hell in order to find him.