- To see if there is going to be a mini-boss/secret on a given level look at your turn log when you enter a level. An example is in the 2nd floor at Journey to the Kimon it says: "A dungeon fit for a king." which means that the Goblin King is somewhere on the level.
Journey to Kimon:
Level 1: I hear there are rats the size of dogs down here.
Level 2: A dungeon fit for a king.
Boss: Goblin King
Level 3: Dungeon exploring is torture.
Boss: Hobgoblin Torturer
Level 4: I have a baa-d feeling about this.
Boss: Cyclops Shephard
Level 5: Do you smell burning?
Battle for Stormrise:
Level 1: What's cooking?
Friend: Human Chef
Friends: Zoo animals
Friends: 4 Knights
Dark hearts and evil minds:
Level 1: Is magic just science you don't understand?
Boss: The Alchemist
Level 2: Snakes! Why does it always have to be snakes?
Level 3: The enemy of my enemy is my friend.
Friends: 3x Dwarves, The King and a Weirdo
Level 4: An eye for an eye.
Boss: Eye Stalk I forgot the whole name
Level 5: It's all in the mind.
3 Artifacts: Guldar's Helmet, Breastplate of Guldar, Etheral Shield
Mask of the Boy King:
Level 1: The moon is very full tonight.
Level 2: The tombs look more regal here.
Boss: Skeleton Lyche Prince
Level 3: Raiding tombs is a pain in the neck.
Boss: Vampire King
Level 4: The king is dead! Long unlive the king!
Boss: Skeleton King
Level 5: Behold! The golden walled tomb of the boy king.
Boss: Mask Boy
Tower of Magus:
Level 1: Hubble, bubble, toil and trouble.
Bosses: 3 Witches
Level 2: Out of sight, out of mind.
Secret: Wizzard's Slippers
Level 3: When life gives lemonade, make lemonade.
Secret: Doppelganger machine
Level 4: The hybrid children watch the sea.
Boss: The Deep One?
Level 5: The endgame is afoot.
They Dwell Beneath:
Level 1: Here be dragons.
Boss: Celtic Wyrmling Dragon
Level 2: Never laugh at live dragons.
Boss: Saxon Youngling Dragon
Level 3: Come not between the dragon, and his wrath.
Boss: Celtic Adult Dragon
Level 4: When the prison doors are opened, the real dragon will fly out.
Boss: Saxon Mature Dragon, Friend: Chinese Ancient Dragon
Level 5: So comes snow after fire, and even dragons have their endings.
Boss: Saxon Ancient Dragon
Thanks to Linkshot for helping!