The Frog bonus round rule is one of the many rules that can be applied during the Bonus Round episodes. It is offered when either entering floor 4 or 5.

If Drake was the boss of the dungeon when it was generated, the Frog rule will never show up.

Frog

Any enemy can potentially be the boss of the dungeon.

When the rule activates, the boss of the dungeon is replaced with another enemy that can usually be found elsewhere in the dungeon. This eliminates the normal bosses and any enemies that have already showed up in the dungeon on the other floors.

If the enemy has a Super form, they will show up with the Super form's equipment and dice.

Certain enemies, like Super Gardener, Super Stereohead, Super Hothead, Sneezy, Bully, Handyman, Sticky Hands, Paper Knight, and Mimic, will never show up as bosses.

Each boss enemy now has much higher health as a boss.