In Loop Hero there are a total of 4 chapters with their own unique challenges and boss to fight at the end. There is though a fifth hidden boss hidden in the game that can be summoned whenever you want. This secret Easter egg boss is without doubt one of the toughest enemies you will encounter in the game. This How to Defeat the Secret Boss guide will tell you how to summon it and also beat it.
Before you can fight against the secret boss you must first summon it which can not be done until you have completed Chapter 2, this will mean you will need to have defeated both the Lich and the Priestess. Once you have accomplished this you will be able to set up your loop to summon the secret boss which requires you to set up a U-shaped section of your loop so that several effects will all combine on a single tile in the middle. There are different ways you can do this, the following is just one of them.
Start by placing a Battlefield, Chrono Crystals, and Vampire Mansion cards in a row at the base of the U. Then place a Beacon and a Temporal Beacon as the 'arms' of the U. If you leave an empty path in between the base of the U and an Outpost tile blue sparks will start to appear on the empty path. When you take your next loop through this pathway the boss will be summoned. Keep in mind that you will only be able to summon this secret either before or after the current chapter's boss has spawned. The secret boss in Loop Hero is the Frog King, take a look at our How to Defeat the Secret Frog King Boss
to find out what you need to do to beat this Easter egg boss and also see another method for summoning it.
Check out our How to Defeat the Lich Boss
to find out what the most effective strategy is for dealing with this enemy in Loop Hero.