A little confusion with gravity effects
 

I just saw a cool warp that inverts gravity in the third example level for Violet's new tileset conversion. I'm just wondering... how do you make these cool gravity effects?

They're just illusions; there is a layer with the 'floor' or 'ceiling' or whatever you want to call it, and it has it's x speed set to 1, but it's y speed set at -1, so when you jump, gravity appears to go in the opposite direction.

Exactly. An alternate layer (5, 6, 7, whatever) is given all the same properties as Layer 4, except for a Y speed of -1 and (I suggest) Tile Height. Create the visual appearance of the antigravity area in that layer, either from scratch or by copying it in from layer 4. Then reconstruct the mask of the area in layer 4 as best you can using invisible tiles, except the whole thing is upsidedown - I suggest copying from the antrigrav layer, line by line, except in reverse vertical order, and then converting to invisible by hand. For a foreground, employ layer 1 or 2 and give it the same settings as the first antigrav layer. Finally, lots of trial and error.
(Note however that very few tilesets have antigrav support as detailed as CrysilisV, which is why it was specially showcased at all; most of the time the best you'll get is your head partway into the ceiling like in Mike's first episode.)

But the question is, how do you do it with warps?

...place the Warp Target into the area with the effect.

Well thank you guys for the help. I just might try to make a level like that sometime ;)

(It's cooler without warps, like Mike managed...)

I know ;)

I actually did use a warp, at least to begin the effect. To return to normal gravity there was no warp, but was a lot of visual trickery hidden in an area where the player would normally run through quickly, so it was easy to pull off.