On the editorial page of Dragon magazine number 127, the then editor, Roger E. Moore wrote about what he called Tucker’s Kobolds. The complete text of the editorial, either legally or illegally can be found here. When I first read it in late 1987, it sparked the idea of what I called Castle Kobold. The idea behind the dungeon was simple, kobolds, swarms of kobolds, so many kobolds even a 12th level paladin would have trouble killing them all. Some were clever, most were not, but what ultimately gets the characters was not the cleverness of the kobolds, but rather the mathematics of the game. Even if the fighter on point has an Armor Class of -5, the kobolds still hit on a natural 20, which means if 20 kobolds fire crossbows at him, one is going to do 1d4+1 damage, an average of 3.5 point of damage every time he turns a corner, or enters a room. Even a 10th level fighter tended to have between 60 and 70 Hit Points, assuming better than average roll and a decent Constitution. The kobolds will probably kill him in 20 salvos, give or take.
Granted a well placed Fireball will easily clear a room of kobolds and a simple Shield spell goes a long way towards protecting the party. But what self respecting Magic User bothers to memorize a Shield spell and how many Fireballs does he have memorized. Besides that, the clever kobolds will figure out where the Fireballs are coming from and suddenly its not the fighter in glowing plate mail who is getting the salvos of crossbow bolts. The Magic User with 20-25 Hit Points will not last 20 salvos. The bottom line is, even the weak little kobold can be a bastard of an opponent if there are a lot of them, they are entrenched in thier environment and hell bent on defending it.