Ratchet and Clank/Game Mechanics and Glitches

Glitches

Slope-intercepting (SI)

Works in every version of the game
The Slope-intercepting (also shortened as SI) is a glitch that involves the helipack and the geometry of some levels. If you land on parts of the level you're aren't supposed to explore, the game just makes Ratchet slip to the ground when he makes contact on these surfaces (or into anything that can kill you like a void). But on some surfaces, it's possible to prevent Ratchet from slipping by doing a high jump as soon as Ratchet hits the ground. The best way to do it is to hold R1 and mash X as fast as possible so the game thinks you are on a "walkable" surface. This glitch permits to go out of bounds in some levels and can be used to skip entire planets.

Some grounds however are protected against this technique, as they are making Ratchet slipping instantly when he touches them, not letting the player to have the time to do a SI, and blocks the player to do a single movement until Ratchet has reached the ending of the slip (most of the times it leads to death). These grounds are called instant-slip.

Decoy clipping

Works in every version of the game
Requires the Decoy Glove (7,500 bolts)
Decoy clipping is a technique that is widely used by glitchers and was one of the first glitches found in the game. It involves using one or several Decoys in order to clip through walls. It works simply by putting Ratchet into first-person view next to a wall, a door or a barrier, and throwing decoys on the ground very closely to Ratchet so he can't move away from the wall. If it's done correctly, the game will think the decoys are more solid than the wall, and will throw Ratchet on the other side of the wall.

It's a glitch that is still widely used in speedruns, but there is now a route in New Game category that completely skips it : the main reason is the Decoy Glove is quite expensive and the way to skip it is slightly faster than collecting the bolts required to acquire it.

Zombie Ratchet

Works in every version of the game
Requires the Swingshot (1,000 bolts)
The Zombie Ratchet is a state that permits Ratchet to clip through walls without Decoys. It works on two planets (Umbris and Veldin), which both have mud that kills you by drowning. However, the game considers you killed when the entire body of Ratchet is drown. You can prevent this by catching a Swingshot orb : just jump into the mud, and before touching it, use your Swingshot. Ratchet will then touch the mud, drown, but will be thrown out thanks to his Swingshot. When performed, the glitch stays until you die or if you leave the planet.