Superbosses are a unique form of post-Moon Lord bosses that the Calamity Mod adds to the game. They are exceedingly difficult, boasting overwhelmingly high stats, mainly immense health and ludicrous amounts of damage. In certain cases Superbosses also represent a significant departure from Terraria's typical boss formula, such as the Supreme Calamitas encounter being more of a bullet hell endurance battle. Not all of the planned Superbosses have been introduced yet, and will be coming in the future.
Supreme Calamitas is a bullet hell Superboss with 5,000,000 health (8,000,000 in Expert Mode and 8,800,000 in Revengeance Mode). She is currently the only Superboss in the Calamity Mod and the mod's most challenging opponent so far. Supreme Calamitas' attacks are primarily enormous waves or floods of projectiles which are very difficult to dodge, though she also summons servants to aid her.
Her main drop is Calamitous Essence, which is solely used to craft Shadowspec Bars, which can then be used to craft many Developer items. In Expert Mode, she can drop some of the Developer items directly.