First off, you should have kept this in your other thread. Otherwise, thinks tend to look very messy, so next time (don't bother changing it now) keep all these questions in ONE thread, please.
Second off, if you want the Archmage to attack the UNIT that is ATTACKING your red neutral team thing, then I would use a trigger like this:
E: A unit attacks a unit
C: Attack unit is owned by Player <X> Red
A: Issue Archmage to teleport, targeting ATTACKED unit
Issue Archmage to attack ATTACKING unit
That should do it (I think) lemme know what happens.
Oh, and read the rules, and you'll understand about the first part of my message!
-Forgot this-
Abilties can be edited in the OBJECT editor...I think it looks like a button with a helmet, from your main Warcraft Editor window. However, if you have RoC, you have a problem, because I'm not sure if you can edit/create custom abilities...