Blast through is a glitch in Super Smash Bros., Super Smash Bros. Brawl and Super Smash Bros. Ultimate. It involves hitting a character at such high speeds towards a solid part of the terrain that they go straight through. Despite the mechanics around the glitch being simple and with the potential to lead to several instances of the glitch happening, it is difficult to pull off accidentally.
Super Smash Bros.
The glitch is only currently known to work on the Race to the Finish and Peach's Castle stages, and with two characters. A character with sufficiently high damage can go through the surrounding walls of this enclosed stage.
If done successfully, the character should escape from the inside of the stage and be KO'd.
On the Peach's Castle stage, it is performed in a different way, rather than the walls or floors.
If done successfully, the character will pass through the Bumper and be Star KO'd. In Training Mode, however, if the game is slowed down via the speed features, it can be seen that the character collides with the Bumper, rather than passing through it.
Super Smash Bros. Brawl
In Brawl, this glitch allows a character to pass through thin terrain in a stage. It can be done in at least two places:
For the first scenario, if all went well, the opponent should fly through the tip of the Great Fox' fin. For the second case, the character should pass through the structure.
In certain stages, such as a No KO custom stage, if a character is hit hard enough through semi-thin walls, they can end up inside the walls if their velocity is high enough, such as being hit by reverse aerial Warlock Punch, Critical Hit, almost any fully charged forward smash from a character above a weight of 120, Giant Punch, and several other moves that have a large amount of knockback.
There are reports that this glitch can be done on enclosed custom stages. This seldom happens successfully, if at all, however, given the stage builder blocks' high thickness. The hardly-coherent instructions that are most used are roughly as follows:
One of the easiest and least performance-intensive ways to check for collisions is to analyze if a character's hitboxes would be inside the stage's hitboxes on the next frame of movement. If so, then the move doesn't happen, and the character bounces off. If not, that means that there is probably no terrain in the way for the next frame, so movement can happen.
If the speed is too high, the character moves a large distance per frame. Suppose one frame, the character is very close to a piece of solid scenery, and the game calculates their position on the next frame. Due to their huge distance move per frame, the next position is beyond the terrain. As such, the game assumes there is nothing in-between.
This glitch isn't a problem because the Super Smash Bros. game engines check for collisions at least once per frame, which is enough to cover most scenarios. It can only happen if severe amounts of knockback are implemented, and only on terrain that's thin enough. A solution would be to implement a different collision detection method, like one that checks for hitboxes between the before and after positions.
Interestingly, it can be noted in the Corneria case in Super Smash Bros. Brawl that the stage actually shifts the character's trajectory a bit, as if it were refracted. Whether or not this is influenced by the interference of knockback from a small detection of collision on the frame after the pass through, or if this "glitch" is actually accounted for in the engine is unknown.