Some of those tricks are revealed here. We could also work together on some to create new ones.
IF you DO NOT wish to read the description of a trick, just don't highlight the spoiler.

So, here goes a list that's for now pretty short, but I'll add more with time.
Transformation
Effect: Turn Loof into Qookie, or any other character.
Author: Mark.
Method:
Out Of Body ExperienceThis is going to require some cover. You need to hide your Qookie, and you need to hide the moment of the switch.
There is no single method for all cases as per se. One possible way a transformation might seemingly happen (quoted from Mark's Hallucination level) is put Loof at a long ice patch on the start, and put a "big box" model to cover the end of that ice patch. Then make another ice patch (it's start is covered by the big box) so that it seems as only one ice patch. Then put the exit at the end of Loof's ice patch, and put a conveyor at the start of the second ice patch. Put a conveyor timer pressed by a box, and Qookie on the conveyor. After Loof rides the ice, the conveyor should go off, and Qookie will be released.
This really has no single "best method". Find what works for your level.
Effect: Loof is stranded on a very thin ledge, however he soon uses the out of body effect combined with astral projection to invisibly walk over thin air and finally walk through the box onto the next island. The original Loof's body can be still seen, but after walking through the box he also becomes visible. After finsihing this level, and playing others, Loof attempts to use Astral Projection to appear in them as a ghost.

Author: Mark
Method:
TelekinesisThis will require hex-editing. In short, you can put two Loofs in your level with that. The additional Loof cannot be interacted with, but makes for a visual effect.
You also have to make it so that real Loof automatically goes into a teleporter at the VERY start of the level, before the level loads. That means that the game focus will fly way below the real Loof.
Put the additional Loof (the "ghost Loof") such as that the focus will appear so that he is on the center.
This makes for a very convincing illusion that it's the real Loof.
Strand him on one square, so that movements are seemingly unavailable.
Real Loof should be hidden somewhere now (in trees, or fake walls, etc) and has a walkway, which he can use. This makes for the initial "out of body".
Then, put a teleporter at the end of that walkway. Put the other teleporter in the same row in which the ghost Loof is and cover it with a box.
This will complete the illusion.
Effect: Move out of your body but don't appear anywhere.
Author: Me, after being inspired by the previous one.
Method:
Broken!This one is short and sweet. Put Loof on conveyor, and put two trampolines after him (so that he jumps on them) and put EXITS on BOTH of them.
Put Stinky and Peegue somewhere else (exiting on conveyors) to cover the transition. Put a big box to hide the trampolines. Put Qookie at the end of the trampolines.
The result: Qookie is now ghostified, however, the now invisible Loof jumps right into Qookie's ghost. So it looks like you're playing as Qookie, but actually you're playing with (invisible) Loof.
Effect: You've collected ALL the rainbow coins, hear the "ker-ching" sound, see the "Coins: 0 of something" but the stubborn exit gate refuses to open!
To add to the insult, other exit gates can still work happily!
Author: Me.
Method:
This needs a little cover, and a little time to be set up, so make sure that you cannot collect all the coins before it happens.
You've got to set up for a transporter glitch.
Put a box on a moving conveyor. Put three tiles of ice ahead of it. Put another box on the second tile of ice. Put a transporter right after the ice. Put a fiery shadow stinky (and block it from the sides) right above the transporter. Below, put the real Stinky on a conveyor that's five tiles long and starts at the same column as the first box.
What happens is that the fiery stinky shoots a box at a precise moment, and the transporter starts to melt through solid objects. If it melts across a floortile, it will be blocked for Stinky but not for other objects. If it melts through an exit gate, it will be broken like this and will never open, even when all the coins are collected.