Speed tricks

Switch glitch

Discovered by unknown
This is a primary 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 it, 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 continue 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 next trick. However, the method has been superceded by speed preservation.

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.

Speed preservation

Mostly joint discovered by Blublu and KennyMan666
A better variant of the velocity preservation. Rather than not touch any direction, holding down on the d-pad makes your character continue moving at the same speed, even after switching characters. As holding down while walking on regular ground often means your character will start crawling, you need to do a jump to set it up. This allows for the next tricks.

Super swim

Discovered by Aglar
A continuation of the boosted swim, by holding down on the d-pad instead of not touching it as you switch to Freeon-Leeon, the faster swimming speed lasts until you let go, touch any other direction or jump. Useful anywhere the boosted swim was used.

Boosted jump

Discovered by KennyMan666
By preserving Bop-Louie's running speed in a jump with Shades, Shades will complete the jump at Bop-Louie's horizontal speed but his own falling speed. This allows for longer jumps than normally possible and is the basis for the following two tricks.

Boosted bounce

Discovered by KennyMan666
A variant on the boosted jump that involves bouncing off an enemy. There's two lava pits that can be crossed faster with this. The most important is the one before the blue key guardian, the other - only used in 100% - is the pit leading to the door to the red power ring. With Bop-Louie, do a running jump off the ledge and bounce off the enemy, switching to Shades and holding only down just as you hit the first enemy. Shades will complete the bounce at a fast horizontal and slow vertical speed, allowing this pit to be crossed without taking damage without using Freeon-Leeon's secret weapon.

Skipping the light switch

Discovered by KennyMan666
One of the largest time-saving tricks in an any% run. By doing a boosted jump, you can clear the pit in the dark area before the green key guardian without the blocks that appear when turning out the lights, saving nearly two minutes. Most easily done by starting in the room to the left, using Bop-Louie to run and jump then holding down to preserve the speed, then switching to Shades and jumping over the gap. You will then need to switch to Bop-Louie to climb up, as the jump will reach only far enough to touch the side of the ledge holding the chest with the medicine.
Video demonstration

Skipping Shades

Discovered by Blublu
Previously thought to be TAS only, it has been confirmed possible on console to clear the gap you normally need Shades for with Bop-Louie. As it involves two pixel/frame-perfect maneuvers in succession, calling it the single most ridiculously precise trick in the game does not even begin to cover it. While the currently published TAS of the game beats the game without ever collecting Shades, the boosted jump 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.
It should be noted that while this trick is realtime possible, it is not realtime viable. It would very much be a route-defining trick in every category if it was. Any routes apart from what the TAS does incorporating this trick have not been created yet.
Video demonstration

Deathwarp

When you die, you are always returned to the same spot at the beginning of the game when hitting Continue. This can save travel time. Health management is not the easiest thing to do in a console run, however, and while no realtime routes using deathwarping have currently been created, the currently published TAS uses it, and with the Shades skip, a realtime any% route with deathwarps would be very similar up until bombs have been collected.

TAS only

There's one trick in this game that is impossible to do in a console run (even if the Shades skip is near impossible). It's not even used in a TAS, but is included here for completeness' sake.

Infinitely long jump

Discovered by Aglar
The logical conclusion of the boosted jump. 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