Each of the dungeons has an entry cost clearly advertised on the dungeons page, Medium Dungeons are more expensive to enter than Small Dungeons and Large Dungeons are more expensive than both. The harder a dungeon is to conquer, dictated by the Level of the dungeon, the more expensive it is to enter also.
Each Dungeon has a reward multiplier attached to it. The larger the dungeon the higher the multiplier and the harder the Dungeon the higher the multiplier also.
This reward multiplier can range from 100% of the cost to enter the said Dungeon to 500% times the cost to enter the Dungeon.
Each Dungeon has a random number of monsters generated and each of those monsters has a random rarity level generated also, both of these factors combined defines the rewards multiplier for the Dungeon.
The higher the number of monsters and the higher the rarity, the greater the rewards multiplier will be.
On top of this, each Dungeon has a chance to spawn a Boss Monster, with a rarity level higher than the normal monsters.
If this boss is defeated your reward multiplier will be even higher.
If you defeat the whole dungeon, the final multiplier will be calculated based on the Size of the Dungeon, Level of the Dungeon, Number Of Monsters, Rarity Of Monsters, Boss Defeated.
The winning amount ranges from 100% of entry cost to 500% entry cost based on this multiplier.
Losing the battle will result in no rewards, though your heroes will be returned to you unharmed.