Okay, so I was brushing my teeth one day when it occurred to me that I should make a game! So I did. After nearing completion, I ran face first into some big problems with one of the map's shop items, specifically one called Spike Trap (oooh scary). Okay, so I have a few specifications for this ability due to map balance, and just glitch avoidance in general. Before going into the specifics, allow me to elaborate on the concept of the ability:

1) Buy ability (quite a concept)
2) Move a location to the current position of the player's main unit (becoming static)
3) Wait for enemy to enter location (possibly inverted?)
4) Unit(s) in the location are attacked once by a lurker
5) Lurker is [re]moved after the lurker does it's business and location is centered somewhere else to prevent re-use

Okay, so now that the basics are covered, allow me to reveal the restrictions:

1) Lurker must attack once
2) Player cannot have vision of the location before or after the attack
3) Player cannot have more then one spike trap on the map
4) Lurker cannot be placed on sloped terrain (not very likely, so don't worry about it)
5) Location cannot exceed "high ground" level while also being at "medium ground" level
6) Lurker cannot be computer owned (on account of the map's inner workings)

Ew, limits. Yeah, so anyways that's my problem. I tried a few things that didn't work and I'll put them in here just so that you can all see my failure. First I tried to place the location along with a Lurker owned by Neutral, and after the enemy spent the equivalent of 25 deaths in the location, the lurker would be given to Player 1 (me) for fifteen deaths, then removed. However, this didn't work as the lurkers seemed to attack when they wanted, be removed when they wanted, and be given to player one when they wanted. It didn't work too well. I also tried the same thing, but instead of preplacing the Lurker, I made it appear for a bit, then disappear, but for some reason it never even showed up. Also, as a random factoid, all the players have a common main unit, and therefore their own individual lurker location. I haven't tried EUDs yet, and I think I might have to if nothing else works.

If this cannot be done then I'll just invent a new ability and silently take this one to the back room where it will be beaten severely by the delete button.

Your restrictions are rather contradictory:

2. Player cannot have vision before or after the attack
6. Lurker cannot be computer owned

If a unit exists in a location during a 'vision update', the player will gain vision from that unit. The easiest way to avoid this is to have the unit owned by another player, but your #6 prevents that. Given that you need to create or move a lurker to that location and have it stay there long enough to target and shoot at an enemy, it is likely that you will at least sometimes have the lurker existing during a 'vision update'.

So you may just have to live with the fact that the player will gain vision during/after the attack, if #6 is immutable.

Also, if you insist on the lurker being player-controlled, what's to stop them unburrowing the lurker or being a pest with it? You can get around this if you have Burrow researched for some other player, create the lurkers for that player with the Burrow property enabled and then Give them to the final human player, who has burrow Disabled. That means they will end up with a burrowed lurker, but no "unburrow" icon to click (or hotkey) and so the lurker will be stuck underground. This doesn't work if you need burrow to be available to the human player for other purposes, though.

I've already considered this and that is the reason why the lurker is only allowed to attack once, and is then removed. If it has only enough time to attack once, then there shouldn't be enough time for the player to even consider unborrowing it, let alone get it out of the location before the timer is up and the lurker is removed from their control.

Also, regarding restrictions 2 and 6, you have a good point there. I guess I wasn't thinking when I wrote that.

Now, got any solutions ?

It is a rather simple problem:

1. Create lurker
2. Leave lurker in the location for the required amount of time for it to attack once
3. Remove lurker

It's really that simple. You just have to work out how long #2 is and convert it to DCs.

Eh. Okay then. I'm going to go try that (again). Don't close this topic while I'm gone.

Maybe create a burrowed, comp-controlled unit with 1 HP on top of lurker? That way the lurker will have to kill the unit when it attacks, and you can remove lurker when that unit dies.

Okay, I'm back and I got it to work too Thanks guys for your help!