Basically i have the scarabs set up to shoot at an unkillable, blocked off building, and i use them for casting,

When they get in though, they go all in one direction, and never hurt anything.

ive never used em before, so dont really know how to makem attack right, can i get some guidance?

Every time the scarabs get moved to the location you want them to attack from, use the "Set unit order to: Junkyard dog" action. This should cancel out the scarabs' previous target.

Doesnt seem to have an effect. i tried running in the scarabs before they moved, and after they moved. and both before and after, they still simply veer off to the left

Are you sure you've made the trigger run for the owner of the scarabs?

Yea. the person casting, owns the scarabs, and its running in their cast trigger.

Then I've no clue, it worked for me.

The reavers shooting the scarabs must belong to a comp player. You can't apply AIs to humans.
The correct order is:
- shoot
- move
- apply AI

There are several AIs you can apply with different effects.
- Junkyard dog will make them spread out but unlikely to hit anything
- Random suicide mission will make it pick any enemy player and hit its nearest unit
- Strategic suicide mission will make it pick strategicly valuable targets (possibly too far away)
- First pick a target with Set generic command target, then run make these units patrol to send the scarabs to a specific place.

When memory serves correctly you can, after a small wait, give the shooting reaver (not the scarab!) to the player to prevent self splash. The scarab should still follow its previous orders/AIs.

Yeah that works. i only wished i could keep it to the specific player so he could get the exp, without me using triggers to transfer the exp.

Use a binary count off, and transfer the EXP of the computer to the player.
It'll be just like the player killed it. Watch out for splash on the Player's unit that is casting it though. It may be injured.

---------EDIT-------------------
Sorry, DIdn't read that. Why can't you use a trigger?

This is certainly not true. In my experience, they work perfectly. One reason for you saying that may be that you've used the Junkyard Dog AI on a large location moved over the scarabs. If that is the case, use a 1x1 or 2x2 tile location - they should be able to hit anything near them that is not within that location.

i can. i just didnt want to. i dont know what a binary countoff is though :E
i just took the experience that the reavers had, and gave it to the person who casted.

Binary countoff is a method to efficiently do that. The experienced is transferred in 1 trigger loop and with the least number of triggers possible. Read the wiki on how to do it.

Since Junkyard dog can be applied to human players, then I could have humans own the reavers from the start, so that they could get exp or upgrade scarabs, without ever giving to computers, right?

In the direct damage system, since I would be moving the scarabs directly onto target, eliminating wasted time and movement as much as possible, I could just center an inverted location onto the scarab and apply the AI that way.

I'm guessing that they would still hit the nearest target after selecting an enemy, using the same targeting process as Random Suicide Mission)

Is this all correct? Just want to make sure I have my facts straight.