Bosses

Bosses are a superior variant of enemies who are bigger, stronger, and more dangerous. They are also primarily Heroes, whom you can unlock as playable characters by beating them from Tier 3 (World 4 in Normal Mode) and onward. They have special battle mechanics exclusive to them, such as sparing them.

Sparing
Once defeated, bosses may be shown mercy and spared, or they may be executed. Sparing a boss will allow for their character-specific assist for the remainder of the run and grants a 400 orb, but gives up the rewards from slaying the boss. Executed bosses always drop an Epic or higher rarity spell and a Rare or higher artifact. For the rewards screen of an executed boss, a temporary boost of 15 is applied.

The number of boss executions and boss spares determine the ending of the run. Bosses can also spare the player if the player is defeated, which is treated the same as the player having spared them.

Scaling
Bosses are subject to the same health scaling as normal enemies, but are given additional health per world.

Tiers
Bosses also gain special tiering. Their stats are also improved. Normally, bosses start at tier 1 and scale up to tier 4 towards the end of the run, but some Hell Passes increase the tier bosses start at, up to tier 4, allowing them to scale up to tier 7, which is the maximum boss tier. Looping a run also allows bosses to scale up to tier 7.

Lethality & Sparing the player
Bosses may occasionally spare the player after defeating them, them for 200 HP and allowing them to proceed onwards to the next world; they otherwise behave similarly to when they themselves are spared, assisting the player in battles and counting as a spared boss towards the different endings.

Bosses have a hidden lethality value, which represents the chance of a boss finishing off the player after defeating them (And, conversely, the odds of a boss sparing the player):

Certain events will increase this chance (And thus, decrease the chance of the player being spared):


 * Killing a hostage, by 1%.
 * Executing a boss, by 2%.
 * Beating a world, by 1%.

Because of this, it's very unlikely a boss will spare the player towards the end of a run, especially from Hell Pass 11 onward. Final bosses ignore this mechanic and will always finish off the player upon defeating them.

List
Bosses are grouped by the World type they appear in. Each World type has two different potential bosses, not counting the Shopkeeper who can be fought in every zone.