The Vengeful Heart of Ender is the final boss of the Echoing Void DLC.

Lore: After being defeated by the heroes atop the obsidian pinnacle, the Heart of Ender was seemingly defeated. However, after the heroes leave with Archie, the shattered shards are shown to be putting themselves back together, but without the four shards that landed among the island realms, it would never be able to reform itself completely.

The remaining chunks within the ruined pinnacle was found by two endermen, who took it back with them to the end, sending six endersent, who would later become enchanted by the eyes of ender, to de-activate the portal so that no one could follow the remnant of the orb. Within the end, the orb remnant reformed itself to the best of its ability into an imperfect form due to the mysterious energies of the End. This form is known as the imperfect heart of ender. When the heroes defeated the six endersent and traveled to the End, this form began stalking them throughout the end wilds and through the broken citadel.

Finally, when the heroes reached the end shrine, the imperfect heart of ender undergoes a transformation before their eyes. This transformation resulted in the heart of ender's final and perfect form, the vengeful heart of ender. The heroes manage to defeat it, and the last remains of the Orb of Dominance are finally destroyed. The heroes then return to the overworld through an exit portal and celebrate the end of the orb's dominance.

More facts here: https://minecraft.fandom.com/wiki/Minecraft_Dungeons:Vengeful_Heart_of_Ender