Like Goblins, Kobolds have been reworked in the 4th Edition Monster Manual, and I really like the change.
Like Goblins, Kobolds can also shift 1 square with a minor action at will. Kobold Skirmishers and Kobold Dragonshields have an extra ability called Mob Attack. What Mob Attack means is that these Kobolds get a +1 to all attacks for every Kobold that is adjacent to the target they are attacking. You can easily see how this will be bad news for a race that loves to set traps and then swarm all over you in large numbers.
But there’s more. There is the Kobold Slinger who has his special shot. He can hit you with a Stinkpot, which deals damage and and imposes a -2 penalty to attack rolls until you make your save. He can also hit you with a Firepot, which deals damage and then deals a little bit of ongoing fire damage until you make a save. Lastly, there is the Gluepot, which immobilizes you.
So here’s how this goes. First, at range, a bunch of slingers sling you, so that you are potentially at -2, on fire, or immobilized. Preferably, all three. Then, you are swarmed by Kobolds who are getting bonuses for every other Kobold near you. This swarming means that your Wizard or other Controller will have a lot of trouble clearing out Minions with blasts of arcane energy.
While being swarmed, you are still being attacked by the Slingers, who continue to shift to better positions and rain down stink, fire and glue for the duration of the battle.
You’d better hope there is no Kobold Wyrmpriest with them, because as an encounter power which is a minor action, he can Incite Faith, granting all Kobold allies within a close burst of 10 5 temporary hit points and letting them all shift one square as an immediate action.
Covered in poo, on fire, glued to the floor, and swarmed by shifty Kobolds who get stronger the more of them there are fighting you. Sounds like quite the way to die.