I heard more then once that the BWO Demo represent the
best designed missions around. I got curious and opened them up in Fred and searched for some sophisticated Fred tricks that would do justice such a statement. Well, I didn't find much so I thought: maybe it's time to start some
lessons 
to show what's possible with that FS2 editor. Some of the tricks I used in my missions for PXO had clearly to deal with multiplayer-only situations (variable amount of players, different player skills, respawn feature, etc.) that won't ever bother a singleplayer mission designer, but they hold some teaching value nonetheless, right?
Some of the events I would create different today if I had to rework the missions, but done-is-done and the effects I wanted to achieve worked fine anyway (within the given limitations of FS2 and Fred2).
Part 1of the lessons is based on my mission
Breaking the Seal (cet_m03) that looks like one of the favorite valid missions on PXO... maybe cause of a destroyable Sathanas in there?
The situation:
As a final threat for the players a SJ Sathanas (Nergal) arrives and the only capital ships that help the players are a Hecate (Tereus) and a Deimos (Halcyone) - if they didn't get destroyed by a lot of hostiles earlier in the mission. More on these 2 friendly capital ships later...
Now that I didn't want the Nergal to be a sitting duck that waits endless for its destruction - it was clear that it will try to jump out after a given time, so I had to create 2 events for that. In the first I made a variable (NerDep) that should hold the seconds for how long Nergal would stay around. As a basic number I used 1080 (18 minutes).
Another value that influenced the departure was the total number of players - 60 seconds per player looked like a nice value to reduce. Since this check happens later in the mission any players loosing their connection won't actually matter for that value and the remaining players won't have to deal with harder circumstances.
In a 2nd event that got chained right after the upper, I made the actual check for the departure.
One of the problems with multiplayer missions on PXO influenced this departure check too: any mission with a flight time more then 30 minutes may cause unpredictable errors - so my max limit for the Nergal staying around was set to 1740 (29 minutes). And it won't ever jump out under 60 seconds. To add
some realism I made sure that the Nergal won't jump out without not repairing some of its engines first.
To spice it up I added 2 more events that would raise the NerDep time if the players disabled the Nergal and/or destroyed the navigation subsystem at least once.
