I was wondering if anyone knew how to make a trigger that would/can turn a unit invisible and vice-versa. I know you can make units invisible, Example: Line-Tower Wars but I just can't figure out a way to do it. Thanks.

Hide arbiters offscreen or use "disable doodad state" on some units. See the wiki for more info.

How do you hide arbiters offscreen? and I tried the disable doodad state but it didn't work.

Disabling by itself only works on a few things. It can have varying effects on units, for example, some units will cloak but be locked in a certain animation.

I'm pretty sure there's no trigger for making stuff uncloak, but you can make some units cloak with this:

Conditions:
Actions:
Give 1 lightworker owned by Player X at Cloaking Location to (player you want the civ to go to).
Wait 0 miliseconds
Move 1 lightworker to Wherever
Preserve trigger[/quote]

This only works on one unit at a time, and that redisabling a unit after doing this will result in crashing. This does not work on all units, and the units that will cloak (and not crash) vary slightly from tileset to tileset (jungle and badlands are the best, if I recall correctly). Also, if the unit being cloaked has energy, it's energy will constantly go down as a result of being cloaked, and it will remain cloaked if it runs out of energy. Units cloaked in this method also cannot uncloak, even if they normally posess the cloak ability.

Units cloaked through this method must be detected before appearing cloaked. Before they are detected, units cloaked in this way will look normal, except that you won't be able to click on them (depending on the circumstances, this may be desirable). After being detected, they will look see-through like normal cloaked units, and after the detector goes away, they will appear cloaked as normal. Also note that geysers will stay visible after being detected even after the detector is removed (I don't remember if you can cloak geysers directly, but if you cloak an extractor/assimilator/refinery, and destroy it, the geyser will remain cloaked).

You don't need to do "enable, enable". Just diable followed by enable is sufficient.

Also the geyser is not really cloaked, it is more 'absent'. You can still click on it and get the selection circle, but the graphic is gone entirely (not just cloak-distorted). The geyser puffs will still appear to give away it's location. If a player builds an extractor on it, and the extractor is destroyed the geyser will again appear normally.

http://www.staredit.net/wiki.php?article=Cloaking_%28Disabling%29_2&skin=5 for future references

Thank you Unholy, looks like the unit that I wanted to cloak just made the game crash. Looks like I'll have to get rid of that spell.

any burrowing zerg units can be perma cloaked via the arbiter trick FYI, but they will lose their cloaking after you reburrow them. Also, Hydras only crash sometimes based on direction. Usually it's one particular frame which crashes, and you can control which frame is being shown while disabled by ordering the unit to move in a certain direction. Once they are re-enabled, they are usually stable (there are some obvious non-stable ones, like a stacked BC unit Sprite, which flies diagonally, and if you fly down, it will crash because it tries to show a non-existent frame).