EEEAB's Mobs Nameless Guardian Add-on 1.21+

Only one boss awaits you in Minecraft after installing the mod EEEAB's Mobs Nameless Guardian. However, this monster will be a serious enemy even for experienced crafters. Therefore, gather the most powerful equipment and head out to the deadly battle with the Nameless Guardian.

Characteristics
Health: 350
Defense: 10
Damage: 15-30
Appears in caves of cold biomes
Has vampirism: each hit drains the player's life and adds it to the boss
The lower the health, the more frequently it attacks