Creatures are mindless or unintelligent monsters or beasts that have chosen to lair in your dungeon. They’re not under your direct control, though they fight off invaders in defense of their lairs. A crafty Dungeon Lord or minion might be able to trick or goad them into doing something for them, though. They're neutral towards other dungeon denizens for the most part, though a bad calamity roll might bring them into conflict with each other. Monsters moving past or through their lairs generally go unimpeded.
Creatures are rated from tier 1 to tier 4, representing how deadly they are. A creature might be a single monster or it could be a group of smaller monsters. When an invader passes by the entrance to their lair or moves through it, the creature engages them and defends its home.
When adventurers pass near a lair's entrance, they're drawn inside. When adventurers are in the vicinity of a creature, it will seek to defend its lair. You roll a creature's tier to determine how a fight goes.
Failure: The creature is slain or flees the dungeon for good.
Mixed Success: You damage an adventurer of the GM's choice and the creature is knocked out the fight.
Success: You damage an adventurer of your choice. Roll again.
Critical: You damage two adventurers of your choice. Roll again.
*You cannot damage the same adventurer twice in a row unless they're alone.
Creature lairs attract creatures looking for a home to your dungeon. When your Dungeon tier increases, you add a new creature lair somewhere to your dungeon. The new lair only attracts creatures equal to the Dungeon tier when the lair was added. When you have a vacant lair, one new creature can be attracted to your dungeon each recovery phase. This always fills the lowest tier lair first.
However, when you first build a lair, it immediately attracts a new creature. You can decide which creature is attracted to the Dungeon. If you wish to refill Lairs quicker, you can spend gold or take downtime actions to attempt to fill vacant lairs faster.
The initial lair, the dungeon tier increasing, and discoveries are the only ways creature lairs can be added. If you manage to come into control of a creature besides those gained in the above ways, you can place them within your dungeon but once they're dead, you lose them forever.
Additional creature lairs can't be built as your hoard can only support creatures determined by the dungeon tier or specific, self-sufficient lairs that already existed underground that you discovered.
Creatures are generally quite unwilling to venture outside of their lairs. If you do manage to coax a creature out, its effectiveness in whatever you're doing with it is determined by rolling its tier as a fortune roll.