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. 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.

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

For all non-event bosses, with the exception of the Lunatic Cultist, 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 Old One's Army, 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 at the bottom of 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 7 pre-Hardmode bosses, only 6 can spawn naturally in a world, as the Eater of Worlds is exclusive to worlds containing Corruption, and the Brain of Cthulhu is exclusive to worlds containing Crimson.

Hardmode bosses
Hardmode bosses are significantly harder upgrades of and new additions to previous bosses. Defeating them is usually instrumental in advancing the game in some way. Each has its own particular way of being summoned, and warning messages appear whenever one is about to appear. Defeating a boss concludes with a congratulatory message and several items.

During Hardmode, each night has a 10% chance of spawning one of the three mechanical bosses that have not yet been defeated in the current world. This only happens after removing at least one Altar from the world, so it may be advisable to refrain from doing so if the player is not ready for a challenging fight. A recommendation for early hardmode is to challenge the Queen Slime. It is essentially a harder variant of King Slime, and allows for upgraded equipment. However, the fight is entirely optional, and not required for progressing the game.

After the defeat of the three mechanical bosses, the underground jungle begins to spawn Plantera’s bulb. Taking action against these bulbs will promptly spawn Plantera, a plant like boss inspired by an indie rock band. At the end of the battle, the player receives the Temple Key, which can be used to open the Jungle Temple to combat Golem, gains access to the hardmode dungeon, and Prismatic Lacewings begin to spawn in the hallowed biome, which summon the Empress of Light. Following Golems defeat, the Cultists spawn outside the dungeon, effectively opening up the path towards Moon Lord, which is considered the final boss of Terraria. It is also recommended to take on Duke Fishron at this time, although available at the start of hardmode via the Truffle Worm.

Event bosses
Event bosses are classified as mini-bosses.

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