Introducing new players to a Campaign mid-adventure

Question

I am running a campaign where all of the players are members of an army, and the small group acts almost as a form of "special forces" in this Pathfinder campaign, taking on enemies that no one else can defeat.

Now I have lost two players right as the party is in the middle of a cave system, before a major boss fight, and I'm getting two new players. The boss is a dragon with some of his servants, in a completely unexplored cave system, in the middle of a dangerously frozen tundra. How do I explain the loss of the two old characters, and the sudden appearance of the two new characters?

Since they are supposed to have been lost, it is out of the question that the players have been given backup, and they are fully healthy in a small cave, so just suddenly killing them off would make no sense. And it is impossible to give them sudden reinforcements. I don't like to retcon since that always seems like a missed opportunity for a good plot twist — I always feel like I've cheated when I use retcons.

Answer 1

By complete and utter coincidence, combined with a little bit of incompetence in leadership, the new players show up at an opportune time. As it happens, there were two groups assigned to do the current party's job, but nobody realized it until both groups had been sent out already.

The first group is the current party, and was assigned to this task by (the king? his spymaster? his top general? his other top general? the captain of the palace guard? a scheming duke?) The second group consists of the new players, who were assigned to this task by somebody entirely different. (If you want to be complicated, have the second group be there for a different reason. Make up another reason for them to be there. The players haven't explored the entire cave system yet, so you can still add something in an area they haven't seen.) If you think that "just the new players" is too small of an adventuring party to take on this cave system, then the new players' party was once larger, but some people got killed along the way.

As for how to dispose of the characters that left the game: adventuring is dangerous. People die, sometimes with no warning beyond "Hey, what's that funny soun---". Death doesn't respect character back-stories or plot arcs or convenience; if somebody suddenly has a gaping hole in their larynx, being in the center of a web of plot won't help them. Of course, if your players have easy access to resurrection, then that won't fly. So, if you truly need a way to remove the PCs without killing them, then the second group could have orders for the PCs who are leaving, that are more important than their current task. Or an offhand comment by one of the newcomers makes one or more of the PCs suddenly run off to rescue a loved one, who was living in a city that just got besieged by an invading army.

Note, if you kill the extraneous PCs, and you make it a "deus ex machina" moment, make it clear to your remaining players that you're not going to kill them that way while they're still playing. Most players don't find it at all fun when the GM randomly kills off PCs; don't let your players pick up the idea that their PCs may suddenly be taken from them if they annoy you.

Answer 2

Since it sounds like you're at the end of the adventure, one option is to talk to the new players, explain the situation, and ask if they're comfortable running one of the old characters, just for the final boss fight. Afterwards, the old characters retire, and the new characters join the group.

This allows you to retain coherency in the story, doesn't provide the existing characters with backup / reinforcements (as that is impossible based on your requirements), doesn't straight-out kill the characters of the now-missing players, and allows the new players to begin playing immediately.

The obvious downside is that you're asking the new players to play characters they didn't design and have no emotional connection with--which can be inconvenient and disappointing to them, so be clear that it's completely up to them whether or not they play the old characters. You'd have to bring the new players up to speed on what has happened during the current adventure, as well as the personalities of the characters that they'd (temporarily) be running.

Answer 3

In the night before the boss fight, a portal opens. Older versions of the remaining existing players step out, with the two new characters in tow.

Maybe the new guys are bound, gagged, and are thrown on the floor, with the one of the existing player's saying: Here, now prove you are worthy to live.

Or they come in by free will, packed and ready for war, having been hired specifically for a dangerous expedition into a cave.

Either way, before the now-versions of the players can do anything, the old versions step into the portals again, and the portal vanishes.

Alternatively, you could also have a known npc, best a previous minor antagonist, bring the new guys - making everyone wonder, why, suddenly, he would help them...

Answer 4

It is all up to you, as GM you are god and you make the rules. You could say the older characters died and the leader of the army sent you new people to fill in. He really needed this quest completely and gave you the extra man power to get it done.