Crutch Character: A particularly horrid example. You need them in order to win in the first stage...then they are entirely outclassed by stronger units as soon as the second level.
Bile DemonsWhile slow, the bile demon is still an excellent fighter, and manufacturer. They are immune to gas and wind attacks, but are vulnerable in combat to most types of undead.
Arch-Enemy: Skeletons. The rivalry can be dangerous if it's an experienced Bile Demon and Skeleton; a Bile Demon is more valuable than a Skeleton, but a trained Skeleton gets Lighting Spell that can kill the Demon.
Big Eater: If a Keeper is planning to have any number of Bile Demons, they better have a large Hatchery. Most minions will eat 2-3 chickens for a meal. Bile Demons eat 6 at a time, and they're hungry often.
Dark MistressesThe kinkiest of all creatures, one who enjoys pain and inflicting it on others. She has no special job apart from visiting the torture chamber to be tortured. Slapping her makes her happier and she rushes off to a battle as soon as one starts. An excellent fighter.
Sex Is Violence: These ladies go for the "moaning after being hit" approach.
Too Kinky to Torture: They put themselves in the torture chamber for fun. If you capture an enemies mistress and torture her, she'll join your side out of gratitude.
Torture Technician: Mistresses are experts in the many arts of torture. The second game has these degenerate dominatrixes assist in "convincing" victims in the Torture Room.
Villain Teleportation: At level 10. Which is what makes it difficult to keep them out of the torture chambers.
Demon SpawnA fairly good fighter, that can walk over lava unharmed. Spends most of its spare time training. After your demon spawn trains to level 10, they continue training and level up into a level 4 dragon.
Crutch Character: Effective throughout the early levels. Later on, outclassed by stronger units, especially when you can get Dragons right off the bat.
DragonsThe dragon is one of the toughest creatures in the game. Quick to learn from training, and a good resource in any library. As you would expect, they are immune to the effects of lava, and actually gain experience from sleeping next to it.
Our Dragons Are Different: Starts out as a little monster, grows into a big dragon after some experience. These Dragons also enjoy a good book.
Stone Wall: Their damage output, with their Flame Breath, is actually very low. However, they have high health and Heal, which allows them to survive for long periods of fire.
FliesThe fly is a weak fighter and does not last long in battle, however they are a very fast unit and great for exploring as they can fly over water and lava.
Big Creepy-Crawlies: Despite the uselessness of this species, they are giant flies sentient enough to seek employment.
Fragile Speedster: Doesn't even have the strength to make up for their low health. They tend to fall out of favor later in a Keeper's career for this reason.
Too Dumb to Live: A Fly's sole purpose is to buzz around and reveal the map to its Keeper. If it finds any enemy along the way, it'll attack on sight. Flies are incredibly squishy even at high levels.
Averted however if "Flee" is toggled on, which orders the Keeper's minions to flee from enemies too strong for them. Which... makes Flies surprisingly effective early, as they will constantly harass enemy imps while fleeing should the enemy Keeper attempt to stop it with stronger creatures.
GhostsWeaker than the skeleton in fighting ability, the main use of the ghost is in research. Given the chance, these creatures will tend to congregate in your temple and will need manual duty allocation. Ghosts can fly, see invisible creatures, and are immune to poison gas.
Our Ghosts Are Different: The only way you get these lost souls is by torturing people to death. They are then subservient to you, oh dark one.
Horned ReapersThe Horned Reaper is the most destructive, psychotic fighter of the game. Summoned only using your temple, they are one of your fastest creatures, and have the power to slow any enemy fighting them. The reaper is immune to lava and has a good field of vision. If allowed to get annoyed (which happens very easily), they will go on a general rampage. It's best to build them their own personal dungeon, behind a locked door.
Awesome, but Impractical: He's easily the most powerful creature you get, unless you get the Avatar on your side, but he's just as likely to attack you as the enemy.
Ax-Crazy: It wants nothing more to kill things, be they the enemy or your own minions when it's really angry.
Lightning Bruiser - Bile Demons and Dragons may outlast him, but the Horned Reaper's offensive strength is unmatched and his speed is above average.
Psycho for Hire: One of the finest examples. One of the better strategies for keeping a Reaper happy is to build him his own little dungeon, i.e. putting him in solitary confinement. Having the entry corridor be completely full of locked security doors is optional.
Unstoppable Rage: As soon a Keeper's Horned Reaper snaps, he is not coming back. He will not stop until you, your minions, and your entire dungeon is broken and bloody. Or he's dead.
HellhoundThe hound is a good fighter and has the ability to travel safely over lava. Hounds will tend to follow your more powerful creatures around as bodyguards, but will attack your own Demon Spawn if given the chance. Placing Hounds in your graveyard will speed the appearance of Vampires.
Leeroy Jenkins: Has the same duty as the Fly, but is specifically looking for things to kill while it's running around. And just like the Fly, it won't hesitate to attack enemies despite relative strength or numbers.
Urine Trouble: A fittingly dark usage of the trope. Hellhounds will do one other duty, which is to urinate on fresh corpses in a Keeper's Graveyard. This makes the bodies decay faster, leading to quicker Vampire production.
ImpsThe imp is the basic laborer, who carves out your dungeons, mines your gold, reinforces and decorates your dungeon, and carry things like bodies and traps around. Imps are the only creatures that give their loyalty for free, and are also the only creature that can be created magically, however the price to create an imp increases with the number you posses.
Fragile Speedster: A little time spent dodging spiked balls in the Training Room, and these little guys can cast Speed on themselves. Especially experienced Imps can teleport at will.
Worker Unit: Nothing will move in your dungeon without Imps. Other minions are too lazy to dig gold, set traps, reinforce the dungeon walls, or build rooms of any description.
OrcsThese are good all round warriors and like to be allocated guard room duties. They are quick to learn from training, and form a good basis for any close quaters combat. Orcs will refuse any research based duties.
SkeletonsThe skeleton is another good fighting unit at high levels, and they are attained when a humanoid creature starves to death in your prison. Skeletons advance quickly when trained, and are immune to the effects of poison gas.
Harmless Freezing: Sufficiently high-level Spiders learn a Freeze spell that they will happily use in battle. When they have no assigned tasks, they will meander to the Keeper's Prison and freeze the captives within. This has a side effect of making the prisoners live longer without input from the Keeper.
TentaclesThey hit quite hard and are fairly tough, which make them good fighters when combined with their freeze ability.
Our Monsters Are Weird: A creature with three tentacles for legs, and one for a head. They have no eyes of any description whatsoever.
TrollsThe troll is best used for manufacture, and has been known to turn down less manual jobs, such as research. Initially poor in combat, the troll gains good firepower at later levels. However, they are unlikely to use range attacks unless possessed.
Non-Action Guy: Trolls prefer to spend all their time at the Workshop and won't bother with much else on their own. That being said, a prudent Keeper will train Trolls for a last line of defense.
VampiresThese undead creatures are vicious fighters and very skilled scavengers. They prove good researchers but will refuse to stay in your workshop. After a vampire's experience is above three, it becomes immortal, and can resurrects itself in its Lair after it dies, at the cost of 1 experience level. As with other undead, vampires can see invisible creatures and are immune to the effects of poison.
Arch-Enemy: With Warlocks. This can be halfway prevented by not letting either group share facilities in the dungeon.
WarlocksThe Warlock is good at both research and manufacturing, has a good range of attack spells, and gains vast experience if their lair is placed next to an unmined gold square. Unfortunately, they are also poor in close quarter combat.
Arch-Enemy: With Vampires. They're presumably jealous of their immortality.
Berserk Button: Warlocks are infuriated by minions (especially imps) wandering into their library while they're researching. If they're at least level 2, they will cast fireballs at the offending minion, often killing them if they're an imp.
TunnelerThe equivalent of your Imp unit, Tunnelers lead parties of stronger Heroes into your Dungeon, clearing their path to your Dungeon Heart. They are easy to dispatch, and even the weakest of your Creatures should have no trouble vanquishing them.
ThiefHuman units that are easy to kill, and are often encountered with Dwarfs. They will rob you of your gold if they make it to your Treasury and will turn into a Level 4 Knight when trained to "Level 11".
Lovable Rogue: Presumably how they're viewed by the Heroes. To a Keeper, Thieves are grubby little annoyances that aim for your gold.
ArchersLook similar to Thieves, and are basically the same unit strength and usefulness-wise. Archers have a wider range of abilities, however, and can fire Navigator Missiles as well as Arrows.Wizards
Archenemy: With Dark Mistresses. This is very, very bad in the scheme of minion rivalry. Both will attack each other on sight with intent to kill, and both are extremely valuable minions when leveled appropriately. It will take some deliberate dungeon design to dissuade daily duels.
KnightA.K.A. The lord of the land. There is one knight per level unless you train a thief past level 10.
When All You Have Is a Hammer: They don't have any kinds of spells or abilities at their disposal other than their swords... which they are extremely skilled with.
HornyThe Horned Reaper, returning from the first game, but is now a single demon which is called "Horny". He's even deadlier than in the original game, as he can't be damaged. Rather than appearing through a portal, you use a spell to call him in. He's actually needed for the final level as he's the only creature than damage the Stone Knights.