[JLV]

Originally, I did something fairly similar to the original D&D concept for this, but dropped it for two reasons. One, most D&D style wandering monsters are incredibly lethal in TFT, and the party already had enough trouble surviving as it was, and two, given that lethality, I didn't need to harass the party nearly as much as D&D needed that sort of resource and time "sink" to weaken the party.

Later I adopted a technique from the computer game Diablo, which I found worked quite well. Basically, I "stationed" a "wandering monster" at some particular point in the dungeon, and then gave it a radius in which it would freely roam and engage targets, but beyond which it wouldn't normally go. (This also works extremely well in the wilderness.) So you might have a Cave Bear, say, in room X, but it won't go more than, say 10 or 20 or 30 hexes (I use megahexes in the wilderness) from it's starting hex. However, if it catches anyone within it's zone of control, it will attack and/or pursue them until they leave it (and if it's close enough, it will pursue them beyond it -- much like the county sheriff can chase you beyond his jurisdiction if he's in "hot pursuit").

Of course, the "wandering monster" WAS the monster, so you wouldn't normally find a wandering giant lizard in an area which also had a room full of Orcs (unless the Orcs were trapped there by the Lizard, in which case, that's a completely different thing).

The whole concept worked well, because it improved the "logic" of the dungeon for the players and also made the whole thing feel more organic -- especially when, as you were fleeing the Cave Bear, you crossed into the Giant Lizard's "territory" and it too gave chase (or sometimes, stopped to fight the Cave Bear -- but you could never count on that happening!).

Of course, when you killed that wandering monster, its entire Zone was free -- at least until something else (or several somethings) moved into that area and took up residence there. Which would eventually happen, if you wait long enough. In this case, though, Zones would be repopulated based on their proximity to "uncleared Zones." Meaning that if you cleared several zones, the ones closest to zones which still had their monsters in them would be repopulated first -- either by a monster of the same type as was in the uncleared zone (offspring, or tribe members, or something similar), or by a creature that was fleeing the populated zone (a lesser creature that the other one looked upon as food, or something similar). Similarly, cleared zones close to an entrance (whether the players knew about it or not) would repopulate more easily than ones in the heart of the dungeon would. The upshot was that *usually* the new monster(s) would be weaker than the preceding one, and the Players would find it easier to traverse the previously cleared areas than they would entirely new (to them) areas. Though, admittedly, occasionally I would throw them for a loop and have something big and bad move back into an already cleared area -- gotta keep them players on their toes, ya know!