Entering combat is pretty simple.
As soon as it begins, move the "out of combat" character(s) near the fight. Check enemy LoS (left shift). At this point you have two choices.
1) Wander into their LoS, which will put you into the fight, at a later point in initiative. I'd have to double check but I'm almost certain they can't act during the 'current' round.
2) Do something which will affect combat, before you are seen. Shooting them, casting something offensive... If you have invis (Imp/Qasit) ability, or trust your sneaking, you can go into their LoS zones. If you are detected you will be basically choosing option (1). If you succesfully sneak up to them, or are able to jump into a blind spot, your "affect combat" can be a melee attack. This will give you an action on the initial round, although your initiative will still have to be rolled.
It does feel a bit wonky, especially as your "out of combat" characters can move WAY further than allowed during a combat round, or take multiple actions (drinking potions, eating food, equipping gear, buffing people that aren't in the fight yet), because they are not in 'Combat Time'. This allows you to set up very strong ambush style scenarios, even when combat is started with just one person (Rogue) wandering around by themselves in the distance. Its almost as if you get to say "Actually when the fight started I was standing over there" as long as you can actually reach "over there" without being noticed.
