Lurkers' attack range is 6, so you will want a 12x12 location.

Also, you only move the ling under the marine when the ling is no longer under the marine. That means the marine pauses every 15th frame or so, rather than every other frame when moving at full speed. It's not much of a disadvantage at all...

Pyro, the slowdown of the Marine is only "incredible" when you center the ling every trigger loop. Rockz and I mentioned methods that make the slowdown negligible.
And using a cloaked unit is out of the question since it will always block your way. Also, cloaked units too, have a visible death animation, while imo a blood stain is quite believable if you have just been pierced.
However it would be possible to use a stackable, cloaked ghost. Don't know if that would also cause a slowdown. But my intuition says yes.

Alright, 12x12.

The disadvantage of moving the ling only when necessary is that you need a 2nd, larger location so you recenter the right ling, which could cause the "wrong" ling (of another Marine nearby) to get centered. So to avoid that, maybe you should create a new ling and have a seperate trigger remove the useless lings. Although I'm not sure if creation of so many lings wouldn't cause lag.

Thanks guys! These are some awesome replies!

btw, Pyro. The "Rope" thing is the Smokers tongue, if you haven't noticed it comes out of his mouth. xD

I don't necessarily know if I want the scarab effect, although it would work, remember that the lurker is constantly moving, so I would also need the scarab locations to constantly move with the lurkers location, but the scarabs location couldn't center on anything, so it would just randomly go everywhere.

Mind you guys, I've only been map making for a couple of months, the most advanced thing I've done so far is a Defense game like Tofu Defense, and a Cat vs Mouse game, most of it was trial and error and looking at other maps triggers to understand what they do.

I'll see what I can do, but for "Mobile Grids" and "EUD" that stuff is completely new to me, so it'll take me awhile to understand what they do.

Don't bother with EUDs. They're a fancy term used to describe anything you can't do with normal triggers. While powerful, they are often times useless and impractical.

As for the problem with centering the ling, if you only have 4 players, you can use p9-12 to differentiate the lings, and use devouring one if you need more/some other unit. Defiler would probably be best due to the lack of computer being able to use them properly.

This is what I'm thinking so far, I haven't totally begun making anything yet, I have sketched out the map layout, and I'm seeing what kind of units I can get for the best outcome.

At first, I was thinking "I should make them all the same unit, to show that they were survivors" but that would look sloppy and unprofessional.

Starting Level Guns:
- Starting shotgun
- Starting Uzi

Later upgrades:

- Assault Rifle
- Hunting Rifle
- Auto Shotgun

I may use 3 ghosts, and 2 marines. Sure, I guess I could use Duran/Stukov/Ghost and Marine/Raynor.

The terrain will most likely be installation, because the first campaign is all based on a city, and I will need to have the most "City" looking terrain possible, the second campaign is a rural train station setting, so I will need grass/installation for the second part.

If anybody here has played Left 4 Dead, I would like any ideas or suggestions you could give me.

There is a simpler way: use a moving invisible wraith to move the marine towards the lurker.