Bosses

Bosses are aggressive, resilient enemies that offer a substantial challenge to players. Defeating a boss is usually instrumental in advancing the game in some way or another, for example, granting the player a new material for a pickaxe of a higher tier. Each has its own particular way of being summoned. For example, most bosses have associated summoning items that can be used to spawn them manually under certain conditions, while there are others that will appear after the player interacts in a certain way with the environment. Event bosses will only appear during their respective events and leave when the event ends. Mini-bosses also exist and appear only during special events, expressing the same amount of difficulty as many normal bosses. Their health has a huge range: On Classic Mode it ranges from 1,000 to 145,000.

Most bosses and mini-bosses can pass through blocks of all types, with the exception of King Slime,, , body, and the.

For all non-event bosses, with the exception of the, status messages will appear when that boss is about to spawn or has already spawned. Upon spawning, its particular theme music plays. During events, bosses and mini-bosses can appear multiple times and have no distinct spawn message. In the case of wave events like the Pumpkin and Frost Moons and the, status messages that appear at the start of each wave can indicate whether or not a certain boss or mini-boss will appear. Defeating a non-event boss concludes with a congratulatory message and several reward items.

On the, bosses will appear on the minimap, each with an individual map icon. On the, a boss health bar will appear on the screen (it will only show the health of the most recently-attacked boss, if there are multiple).
 * However, bosses will still appear as the standard purple blob that signifies enemies on the.

Pre-Hardmode bosses
These are the first bosses the player can encounter. Usually, defeating one of these bosses will give the player items and materials necessary to progress in the game, eventually leading to Hardmode. Although there are 8 pre-Hardmode bosses, only 7 can be spawned in the same world, as the Eater of Worlds is exclusive to worlds containing Corruption, and the Brain of Cthulhu is exclusive to worlds containing Crimson (assuming the player does not place an alternate evil in the same world as the other one, e.g. via seeds from another world or seeds purchased from the Dryad in Hardmode, and does not use a ).

Hardmode bosses
Hardmode bosses are significantly stronger than previous bosses.

Event bosses
Event bosses are classified as mini-bosses, except for the Celestial Pillars.