The mod currently adds twenty-seven new boss encounters. Many also drop Lore items, usually explanations about what they are and why they exist. The initial defeat of bosses (both vanilla and Calamity) typically results in some form of change within the world, be it new enemies appearing or a meteor crash, indicated by status messages to direct players towards the new content. Most require the use of boss summoning items in order to spawn, but others have more unique prerequisites. The Calamity Mod expands on the number of bosses that can be challenged throughout the game, each featuring unique AI and drops. Mini-bosses also exist and spawn naturally in various biomes under various conditions, which pose a lesser yet still difficult challenge for unsuspecting players. Event bosses will only appear during their respective events and leave when the event ends. 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. Each has its own particular way of being summoned. Defeating a boss is usually instrumental in advancing the game in some way. Bosses are aggressive, resilient enemies that offer a substantial challenge to players.
