Shellshifting or "SSing" is an advanced technique for Squirtle users in Super Smash Bros Brawl. It gives Squirtle's ground movement unlimited possibilities just like a wavedash. There are many applications to SSing that greatly improves Squirtle's offense as well as his defense.
How To Shellshift
SSing is actually quite easy to get down, but applying it is where the skill comes into play. To do a SS, just dash in any direction and quickly press the opposite direction. The result is that Squirtle slides backwards without any lag to follow up with an attack. The longer you hold the opposite direction, the longer the SS, and by just lightly tapping it, you can stall yourself momentarily.
Applications
Standard Attack And Aerials
Coming out of SSing you can do virtually every attack and jump so even short hopped aerials are possible. 3 very prominent attacks out of SSing are Squirtle's standard A natural combo, Shffl'd fair and shffl neutral aerial. All three come out very quick and have good knockback. The shffl fair can be combined with SSing to produce the wall of pain effect.
Shellshift Dancing
Shellshift Dancing or SSD, sometimes called shell dancing can be used for mind games as well as making shellshifting very versatile. To SSD you must first do a regular SS and as Squirtle is coming out of his shell press the opposite direction. This will cause Squirtle to do another SS in opposite direction. Just repeat this and Squirtle will be sliding back and forth in his shell just slightly coming out each time. This works best if you hold each direction you shift in until it is time to shift again.
Shellshift to Grab/Dash Attack
Two attacks that are especially good are Shellshift Grab or shift grab which makes Squirtle's grab ranges massive(one third of Final Dest.) and shellshift dash attack or just shift attack which also adds distance to Squirtle's dash a attack. Simply press either A and the direction you are shifting to do a shift attack or press grab out of a SS to do a shift grab.
Pump Slide
The Shellshift to Pump Slide or SSPS is the greatest application of the shellshift technique and is somewhat difficult to pull off perfectly. It allows Squirtle to slide across a tremendous distance (almost all of Final Destination) and do his Up Smash attack. To initiate a SSPS, first do a complete SS (the longest possible slide you can get) and then perform a jump-canceled Up Smash. If done incorrectly Squirtle will just slide a small distance and do his up smash (a regular dashing Up-Smash, or "Hyphen Smash"). It is easiest to do when Tap Jump is turned "on," as the game will register a canceled jump automatically upon performing the up-smash command. However, it can also be done by pressing the jump button at almost the exact same moment as A (the C-stick should not be used). Although the jump technically registers before the Up Smash, it should feel as though the player is pressing the buttons at the same time.
If performed correctly, there are a few ways the maneuver can be put to use. One way is to leave the smash uncharged, which will release the move at roughly the middle of Final Destination while Squirtle himself slides the rest of the distance, making for a very quick mid-range kill move. Another way is to charge the Smash so that Squirtle takes it with him to the end of the stage, releasing a more powerful eruption of water over a longer distance. Either of these methods can be used to simply give Squirtle some defense as he attempts to cross the stage more quickly than either his dash or his Withdraw move would allow.