Shunkan IdōKamehameha, also referred to as the Warp Kamehameha or the Instant Kamehameha in Dragon Ball Z: Budokai games is Goku's technique which is a combination of his ability to teleport and his signature ki blast. Because of the way it is performed, it is almost impossible to avoid and inflicts maximum damage (due to catching the target off guard). In Budokai Tenkaichi 3, when Super Saiyan Goku (End) uses it, the Instant Kamehameha functions in the same way as in the anime, and is fully unblockable.
It was used by Goku during his fight with Cell. Goku charged up for the Kamehameha (up to KA-ME-HA-ME) high up in the air, pretending to be shooting the Kamehameha from there (which would blow the Earth away if he did) and then used the Shunkan Idō to appear right in front of Cell to blast him with the final syllable (HA!). The astounding, sheer power put into the blast was enough to literally vaporize every part of Cell except for his legs. Later, he used this move against Pikkon, only appearing at Pikkon's side rather than in front of him.