One fun thing could be to give each party a weakness that can be found out by careful spying, and utilizing that weakness could benefit the kobolds.

Examples. (Most of these would probably work best on lower level parties)


One part is very loosely connected, set together by a thiefguild sponsor. As such, they don't trust each other, and everyone is out for themselves. By ensuring that one singular member finds a cache of gold when he's off to the latrine, that party member will haul ass back to the surface, as he can now pay off his dealer.
Or, by ensuring that the party finds one apparently powerful, but undividable treasure, the party will be less helpful towards each other, hoping that enough of the others will die off or be weakened enough that they'd be able to make off with the treasure for themselves.

One party consists of nothing but humans, and their strategy to deal with darkness is to have the fighter carry a torch while they shoot everything that gets near him. What would happen if that torch were to go out?

In one party, both the Ranger and the Fighter are hopelessly in love with the party's rogue, and ensuring this persons safety, and suitably impressing them, is their only reason to be here. Could a carefully forged letter cause n-fighting? What would happen is the Rogue is assassinated, but it's made to look like they ran away? Would they leave? And what would happen if the assassination failed?

One party seems to consist only of fighters in heavy armor, but it turns out, two of them are wizards in some kind of very light mock armor, and should be easy to target if you know who they are.

One party are some hopelessly superstitious, but incredibly dangerous barbarians. Could a carefully orchestrated "haunted house"- style trap system make them leave this ghostly businesses behind, and return to the sunlight?

By listening in to one partys fireside conversation, the players might find out that the Party's Druid/Paladin/moral core, has second thoughts about slaughtering these Kobolds. Could their empathy make them stay their hand in a crucial moment? Or could the players, by luring them into a room of defenseless youngling make them convince the party to leave? Or, if they're feeling cruel, could an illusion of a piteously crying little kobold baby lure the poor sap into a magnificently spikey trap?

One party is so large it could almost be seen as an army. But careful spying reveals they are all members of a religious cult, and would turn tail and run the second their leader, a very cunning charlatan, went down. Or maybe putting up effigies that imply that the kobolds cave is actually a temple to their very own god, would lessen their resolve.