Whee! TIme for more random encounter fun!™
Let's get rolling. Last time, it was a wilderness encounter, so this time, let's use the dungeon charts.
OK, the BX table allow for levels 1-8+, so let's roll a d8
roll, roll
A 6! That's Levels 6-7. Now we need a d20 roll.
roll, roll
A 9! That's "Hellhound" Nice!
It says there are 2-8 of these infernal pooches, so let's see what we've got.
roll, roll
3 + 4 = 7! This could get nasty!
Their hit dice are supposed to match the level (6-7) so let's just say they are each 6HD (Saving as 6th level fighters). Let's roll hit points twice and take the higher total for the pack leader.
roll, roll
4+5+3+3+5+4= 24
5+6+3+7+6+5= 32
So we have a 32 hp pack leader and six 24 hp pack members.
These creatures are described as reddish-brown dogs the size of a small pony. Their attacks are biting or breathing fire. BtB, you roll a d6 each round to see what it does (1-2 = fire, 3-6 = teeth). The breath targets one victim and does 6d6 (!) damage (save for half damage). Its range isn't specified in Cook, but the 1e MM says 1", so pretty close (melee distance).
While the random nature of the charts means they could be in any kind of dungeon, I'm going to go Gygaxian Naturalist here and say that the hounds' den is in a chamber/room of the dungeon which has a pool of lava in it, probably from a fissure in the rock tapping into a volcanic vent. The hounds are immune to non-magical fire and highly intelligent, so they would know that most enemies couldn't tolerate the magma. They normally bed down on the far side of the lava from the entrance for added safety.
Now, since this is a wandering encounter, let's assume they are not in the lair. They are hunting the halls or tunnels in a pack, looking for dinner.
Points to remember: They are smart, nasty, dogs. They can also detect invisible creatures within 60' most of the time (75%). If someone was invisible, the hounds might be smart enough to note his presence and pretend to be oblivious until they could catch him out.
Tactics:
The hounds would know the layout of the dungeon. If they are aware of the party, they would fan out and use any side corridors to flank them. A good blast of fire breath would spoil demi-humans' infravision right off. Then, depending on the party's numbers, they would probably target spell casters first (if possible).
If the flanking was successful, the dogs would harry the rear. They'd also be smart enough to finish off anyone who was looking wounded. If the fight started going against them, they would retreat to their lava lair and –if possible– use the hostile terrain to their advantage (knocking attackers into the lava, etc.).
Kills would be dragged off to the lair and feasted upon. One hound is big enough to drag a human being without too much difficulty (provided it's not for miles and miles). Dragging the corpse through the lava would destroy most gear and items as well as cook the meat nicely! The odd trinket might avoid landing in the molten rock and constitute the bulk of the hounds' treasure.
