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. Not all of the planned Superbosses have been introduced yet, and will be coming in the future.
The Adult Eidolon Wyrm is a Superboss with 2,100,000 health (3,360,000 in Expert Mode and 3,864,000 in Revengeance Mode). It is currently the only Superboss in the Calamity Mod and the mod's most challenging opponent so far.