Is it possible to make player 9 attack? Cause I've made him move and patrol but they don't seem to attack. If they could attack others, can you please show me in a quick sample map? Thanks.

They attack if someone attacks them, but they only retaliate for like a second. Not worth trying to do anything like this with him.

Player 9-11 are essentially neutral. They'll follow you if you attack them but they won't attack; this is because they don't have any vision and can't be given any because they can't own triggers. You can still order them around, however.

Edit:
They can actually retaliate but only very very rarely and unreliably.

If the problem is that they don't have any vision, why not place map revealers for P9? Might help him attack a little more

That wouldn't work.

These players don't have vision with themselves so that doesn't help. Try turning the vision off for a computer with itself and it will behave the same way Players 9-11 do.

I'm in the process of making a big list of the things you can do with P9. I have gotten it to attack reliably but not in a useful way yet.

please, do explain how you got them to attack reliably.

Get 5 hunter killers owned by P9, and a devouring one owned by you. Make them all close to you and start the map(start locations obv.) Burrow and unburrow, and attack a HK. They will all attack once, and one of them will continue to attack, although slower than normal. I cant remember exactly but if you move away it will stop attacking and they will all follow you. Same if you burrow again. It's possible it's not reliable as i haven't had time to test everything properly but it worked over 5 times in a row when i tried it. I'm in the process of testing the rest and will say when i've worked it all out.
Oh, and the HK that attacks seems to vary each time. It is also possible that it depends on what number the unit is when you place it on the map. Again, i will test it all.

O_O
sounds like voodoo...

Ok that's good information and all but what I really wanted to do was treat player 9 like a computer, I wanted to use scarabs say like.. the computer reavers attack something by ordering them but the scarabs teleport to another location but I'm guessing that doesn't seem possible with Player 9 and others.. D:

No. Well, not yet.

P9-12 are no full computers. You cannot apply AIs to them nor other trigger actions that affect current player. That, combined with the already discussed attacking problems, (P12 not attacking at all) makes it a pretty tough limitation.

However they are useful as "temporary players". You can order them around and give units to them and back (e.g. for grids, RPG cutscenes, cycling systems, etc.). Most of the complex maps wouldn't be possible without that.

If you need active computer players you will have to sacrifice human player slots.