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.
In the Dragon Ball Super manga, Fused Zamasu utilized this technique to beat down Goku and Vegeta after Vegito defused. He soon after went on to utilize this technique in his battle with Super Saiyan God Super Saiyan (completed) Goku.
Video Game Appearances
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. Majin Buu, Kid Buu, and Pure Majins can use a variation to create a portal to thrust their foot through to kick the opponent when in the air as they would normally use the ground as the medium to thrust their foot through to kick the opponent when they perform it on the ground.
In Super Dragon Ball Heroes, Anilaza's version of this technique is called Hyperspace Punch.