Bosses

In Portal Knights you will face the Greatbeasts, the most formidable beasts in the realm, each in their own twisted arenas. Currently in the game there are 3 Bosses, which players will come across every 10 levels during the game. Each boss will occasionally drop a Recipe for a crafted relic that can be used as a portal to a hard mode version of the corresponding boss.

List of Relic Defense Bosses
Relic Defense bosses were added in the "Druids, Furfolk, and Relic Defense" Paid DLC.

Each boss with spawn in a unique gate location separate from all other lanes in Relic Defense towards the end of wave 5.

List Of Mini Bosses
Mini bosses were added in the The Villainous Update.

There will be quest NPCs on each of the below islands that will give you a quest to defeat the mini boss. Once the quest is complete they will then give you a recipe to re-summon them.

Once you have defeated them they are gone and wont re-spawn when you return to the island.