I'd like to be able to detect which player is missing (or has quit), and make his Hero unit (he has only 1) shared with all players, yet still detecting this Hero as being owned by this missing player.

EDIT: And while we're at it, what's wrong with this trigger? It gives me an error related to the event (something like 'EventDialog')?
http://vgshorts.com/BBCode/BBCode3.php?ID=221

I thought you were good with triggers? LOL!

The error message tells you, in plain english what was wrong with it... You are using an event-dialog, where non exists.

Dialog - Disable (Used dialog item) for (Player group((Triggering player)))


as for the detection of the player leaving and blah blah i don't know...

LOL! Fail from me. I copy-pasted the trigger from elsewhere... didn't look carefully.

Anyways, still needing help for the main problem about sharing units, guys!

PlayerLeaves
    Events
        Player - Player Any Player leaves the game with Any
    Local Variables
    Conditions
    Actions
        Player Group - Pick each player in (All players) and do (Actions)
            Actions
                Player - Turn player (Triggering player) Shared Control On towards player (Picked player)

Tada?

Edit: I might have (Triggering player) and (Picked player) backwards; the wording is ambiguous and the description does not provide clarity. If it seems to do nothing, switch the two players and see if it works.

Okay, thanks. Now, what about if the player just isn't there from the very start of the game?
(I guess it's an easy one, but my brain is off and it's 2 AM.)

It's a little trickier, because there is no "Inactive Players" group; you have to make it yourself. And then you have two pick loops for active and inactive players, which means you need to use a variable on the outer loop to hold the first player group.

Initialization
    Events
        Game - Map initialization
    Local Variables
        ActivePlayer = 0 <Integer>
        InactivePlayers = (Empty player group) <Player Group>
    Conditions
    Actions
        Player Group - Pick each player in (All players) and do (Actions)
            Actions
                General - If (Conditions) then do (Actions) else do (Actions)
                    If
                        (Status of player (Picked player)) != Playing
                    Then
                        Player Group - Add player (Picked player) to InactivePlayers
                    Else
        Player Group - Pick each player in (Active Players) and do (Actions)
            Actions
                Variable - Set ActivePlayer = (Picked player)
                Player Group - Pick each player in InactivePlayers and do (Actions)
                    Actions
                        Player - Turn player ActivePlayer Shared Control On towards player (Picked player)

Again, you might have to swap "ActivePlayer" and "(Picked player)" on the last line there; I can't test this code in a solo game.

Also, I'm not sure if SCII removes all inactive players' units automatically from the start of the game, but be aware that empty slots may have some differing functionality on map initialization.

Thanks.
For information: " Player - Turn player ActivePlayer Shared Control On towards player (Picked player)" was the proper syntax.