Well, I have only seen it done once on a defense where the units can walk all over eachother and such. I dont know at all how this is done and I was just woundering if anyone could possibly help me with this. Thanks!

Umm I only know that if a unit is unburrowed and there are many other units crowded on top of it then all the units will move around over eachother.
Usually it's just a mass of units trying all to get to one place while encountering a traffic jam and no way to go back or any other direction.
You can also do it in those "Zergling Blood" games where you mass your own base and then burrow some units early or late on and they will all be on top of each other. If you unburrow them, it will also make them run everywhere.
Well thanks, but the thing I was talking about involves sprites I think, Its where you can literally walk the units over each other without burrowing or anything, Ex: Marine over ghost or Marine over Marine so it looks like there is only one marine but actually theres more.
I'm just assuming, but it could "COULD" be stack.

You can make marines be able to walk through units. I forget how though...
I think it has something to do with unit sprites. =/
Units usually start walking on top of each other when they are near crystals or scarabs and dont have anywhere to go.
You need to place the unit's disabled sprite on the map, then enable doodad state for it with a trigger, and there ya' go, stackable units.
Also (cant be done with triggers) if you order a bunch of workers to move to a geyser without a plant on it, and shift click a few times, then shift click somewhere else (including attacking) then they go there in slide mode, but if they walk off of their stack they get out of slide mode.
And if you place a powerup on top of a unit the unit trys to get out of the way, but you cant place a pwerup on top of a powerup.
I think that map's in the DLDB Right
hereWhat nuclearrabbit said. I always thought you disabled it and enabled it twice, like trying to make a disabled unit useable, but you can try both.