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.
In Dragon Ball Xenoverse 2, Super Janemba can use Illusion Smash as one of his standard strong combos.