This is a brief guide to performing all the useful glitches I have found so far in Scribblenauts. (A version of this is also in the Speed Solutions "master doc" for All Levels.) Every one of these glitches is fairly simple to perform and does not require hard execution or anything too crazy in terms of timing. Some levels may require pixel-precise setups, but if you are running on emulator with greater than 1.5x window size this should not be a problem. Note that none of these glitches (besides the double jump) are useful in the Any% route, as they take too long to set up if your goal isn't to complete every level.

Ceiling Clip

This glitch was originally found by people on GameFaqs over a decade ago. I thought it was an original discovery when I found it because I hadn't seen the board for this game yet. The space within ceilings, walls, and floors is not solid. You can explore this space by using an Air Vent to push Maxwell against a nearby ceiling, and then placing a solid object between Maxwell and the vent. Basically any object that Maxwell can stand on can be used to clip. In general, a Log should always work for clipping, but if you need something taller you could also use a Statue or similar. Ceilings do not have collision from above, so Maxwell will either have to jump across solid objects attached to the ceiling (as in P3-10), or fly through the space. Maxwell can reach in-bounds any time he goes too back through a wall/ceiling/floor, so you will have to navigate carefully in more complicated levels so that you don't lose progress.

Rope Trick

I have to give credit to the Scribblenauts Wikia for this, since I wouldn't have found this trick myself. Basically, all objects and NPCs have trouble detecting if they should be colliding with a barrier that they are attached to. Therefore, if you use a rope or ropelike object to attach an object (usually the Starite) to a gate, sometimes it will pass through and Maxwell can touch it. This is admittedly quite finicky, but in levels where there isn't much space for the Starite to go, it might work. However, there is a much more reliable extension of this trick: if you attach an object to a gate, and then use a Fan or Air Vent to blow the object against it, it should go right through. Either version of this trick can be used to skip switch and button puzzles, or to skip performing other tasks within the level to open said gate.

Tank Clip

This glitch was discovered independently by some people on GameFaqs shortly after the original release, and arguably the current most game-breaking glitch. There are other glitches that might be bigger, but this is the only one that works in both releases of the game. The Tank, along with a couple of other large vehicles, for some reason can be placed a few pixels into a floor (with a deadzone in between the expected positions and the 'buried' positions). If Maxwell or an NPC rides a tank that is placed inside a floor and then dismounts it, they will fall through. As with ceiling clipping, air travel may be necessary to avoid falling out of the level or entering the wrong place.

Terrain Removal

Ground objects (pond, pit, creek, etc.) are unique in that once they are placed, they cannot be moved. This was probably implemented because placing one deletes the terrain behind it, and the developers foresaw nasty gameplay consequences if this was bypassed. However, for some reason, toggling Identify Mode on and off (tapping the magnifying glass twice or pressing select twice) makes the game "forget" that these objects shouldn't be moved, and so you can simply move the objects as you would anything else, exposing the deleted tiles. As stated above, the inside of tiles are not solid, so extra care must be taken to not fall to the bottom of the level. However, if done in the right places, Terrain Removal can be used to reach the Starite a lot faster. Unfortunately, all ground objects in this game are rather large, and the smallest one I know of right now is the Creek (if there's one smaller than this I would be happy if someone told me!). Therefore, this glitch can only be used if there is enough straight horizontal and vertical space for the object.

Double Jump

This glitch only works on the Scribblenauts Collection rerelease of the game, since other versions only allow for touchscreen input. Jump while Maxwell is running (with buttons), release all buttons, then press jump again. You can hold a direction before doing the second jump, but if you're not fast enough you may not get good height out of the jump.