[PF] Red Hand of Doom question (Spoilers ahead)

[RFLS]

I've run this campaign a few times; never really had a problem adjusting on the fly through at least the second arc. However, (and this is where the spoilers start) my current group just threw a mildly difficult wrench in the works. They tangled with the hobgoblins and Ozzyrandion guarding the bridge. The group was driven off, but definitely left Ozzy hurting a fair bit. This is where things went a little funky. Instead of just regrouping to attack, they sent their fastest player back to Drellin's Ferry for some reinforcements. I put a few Diplomacy checks in the way, and ran the "There's a massive army bearing down on you" encounter a little earlier than the campaign expects, but it was a reasonable request, given that it was for help in protecting the town.

So, the reinforcements are on their way. I gave them twenty men; the rest were required to begin the evacuation (read as: I am completely unwilling to run more NPCs than that in a combat). The problem I am currently having is that, while the players have reinforcements, the bridge guards have also had adequate time to send out for reinforcements, but I can't decide if they would have, how many they would have sent for, and what they would be. Thoughts? I'm currently inclined towards some goblin warriors riding draconic hellhounds, a handful of warlocks, and a few more hobgoblin veterans.

Other thoughts I've had:

Instead of rank and file, have a manticore or two, possibly a chimera show up. My problem here is that this would be an incredibly boring and/or lethal combat for the players.
Abrithriax (sp) shows up to assist Ozzyrandion. This also probably (certainly) does not end well for the players.
A small squad of elite troops, designed to give the players specific secondary targets to Ozzyrandion (also designed to let Ozzy escape if that's the way the battle goes.


For reference, the characters are level six, and consist of:

A pouncebarian.
Snowflake Wardance bard.
Wildshaping druid (he likes bear hugs).
An ineffectual rogue.
An oracle (general buffing).
A sorcerer (rarely present).
An alchemist (focusing on the Explosive Missile discovery).
-unknown- (I killed his previous character).

We have anywhere from 4 to 8 players per session, but I can generally count on having 5 or 6.

The long and the short of it is that I don't want the players' reinforcements to make the battle a cakewalk for them, but I don't know the best way to approach it. Thoughts? Advice?

[KillianHawkeye]

IMO, don't bring any of the other dragons in yet, especially not Big Red or Blue. I would say pull something from one of the "random" encounters that you weren't planning on using, like the barghests or something from the "invade Drellin's Ferry" waves, or I forget what else. Spawn of Tiamat that aren't already scripted into the adventure; there are some that should be weak enough. Goblin worg riders works pretty well in a pinch, too. Go ahead and mix in something with flying like a chimera or wyvern (not another manticore, they already faced one at the keep in the forest).