Speed tricks

Switch glitch

Discovered by unknown
This is the route-defining trick in both the 100% and low% runs of this game. If you have collected a secret weapon for a character that you have, you can use the secret weapon of any character you have without having collected the item. Hold B to charge the secret weapon of the character that has in, then keep holding B while entering the subscreen and switching characters. The charge will be completed with the character you switched to, thus allowing you to use a different secret weapon. In an any%, used to collect the blue key before getting bombs. In a 100%, used to collect everything you need bombs for except the green key before actually getting bombs. In a low%, means that you can't collect any other special weapon, meaning bombs is the only one you get and you have to use the switch glitch to defeat the knight. Have fun.

Triple hit

Discovered by KennyMan666
The knight boss needs six hits from either Bop-Louie's or Shades' secret weapon. Bop-Louie's will hit once. Shades' will always hit twice, but if the eyes are launched while positioned right next to the boss so that one hit occurs nearly immediately after the weapon has been used, they will hit three times. The triple hit only saves time if you manage to perform two of them, as it is only that way you can defeat it with only two chargeups.

Ice jump

Discovered by KennyMan666
When walking on ice with Freeon-Leeon, normally you will have a fast walking speed but a slower jumping speed. By holding down instead of left or right, however, you will constinue walking forwards at the same speed and the jumps will be performed at the same speed as well. Useful in the ice cave and the ice dungeon. This is notably the only trick on this page that was used in the 41:40 any% run currently up on SDA, showing how far this game has come since.

Drown switch

Discovered by Adebis
If you switch characters underwater to one that cannot swim, all velocity, both horizontal and vertical, will be canceled. This allows you to instantly stop with Gil underwater. Has minor uses in the water maze on the way to the bombs and also when getting the blue key in a 100% run, and a major use against the diver boss.

Velocity preservation

If no direction is pushed after switching while moving horizontally and not being on the ground, the horizontal speed of the character will be preserved for a few moments. This is the basis for the three following tricks, the fast swim being the first one found.

Boosted swim

Discovered by Blublu
Jumping into the water with Bop-Louie, switching to Freeon-Leeon before landing in it and not touching left or right will make Freeon swim on the surface at Bop-Louie's walking speed for a moment. Useful in the bodies of water in the mines while heading towards Shades, to the left of the tree area and at the bottom of the tree area. Cannot be used if the water is not at least three tiles deep, as landing in water only two tiles deep will make the character lose all velocity even if you use Freeon-Leeon. Trick superceded by the super swim.

Super swim

Discovered by Aglar
A continuation of the boosted swim, by holding down on the d-pad instead of not touching it during a boosted swim, the faster swimming speed lasts longer. Useful anywhere the boosted swim was used.

Jump extension

Discovered by KennyMan666
The largest time-saving trick in an any% run. By doing a running jump with Bop-Louie and then switching to Shades nearly at the height of the jump but before you start falling, and then not touching the d-pad after switching, Shades will complete the jump at Bop-Louie's horizontal speed but his own falling speed. This allows for longer jumps than normally possible. Useful to cross the lava pits before the knight boss without having to take damage, but most importantly, it allows you to clear the gap before the green key guardian without the blocks that appear when turning on the lights, allowing you to skip the light switch - saving a full two minutes!
Video demonstration

TAS only

There's two tricks in this game that are impossible to do in a console run. They are included here for completeness' sake.

Skipping Shades

Discovered by Blublu
By performing a sub-pixel perfect jump, it is possible to clear the gap you normally need to collect Shades to jump over with Bop-Louie. While this is useless for a console run, it saves a lot of time in a TAS. While the currently published TAS of the game beats the game without ever collecting Shades, the jump extension allowing you to skip the light switch means that it saves enough time that it is worth it to take the detour to collect Shades when heading towards the blue key after collecting bombs.

Infinitely long jump

Discovered by Aglar
The logical conclusion of the jump extension. Due to the way vertical velocity works in this game, it is possible to negate it entirely by entering the character select screen at the right frames, and thereby perform a jump of theoretically infinite horizontal distance with Shades. While it can be used to get the suction cup without returning the egg to the bird, having to enter the sub-screen every few frames makes the jump take a very long time, and combined with that you have not collected Shades at that point in a TAS, it is not used in any run and is only included here as an amusing paranthesis.
Video demonstration