Battleborn

Rendain is the final boss of the game and is an absolute pig. After destroying the large crystals and "saving the universe" in The Heliophage you will be transported to an arena in a different part of the level. Rendain will confront you there, start off by using the jump pads to reach a different "island". Long range characters will have a better time here, seeing as Rendain will use black tendrils to whip you around. He prefers to try knocking you off the platform rather than outright beating you down, so stay away from the edges. Attack from his back and sides until his shield has been depleted, initiating stage 2 of the fight.

This next part is a boss rush mode, pitting you against half the bosses in the game (all of them on Hardcore) using the same techniques you used earlier in the game to defeat them. Warlord Nix can be flanked and attacked by headshots. The Jailer has guards shielding him, which have the same attacks and weaknesses as a regular Beastmaster. Once the guards are dead, the shield around the Jailer drops and leaves him vulnerable to attacks. This process will repeat twice more until the Jailer dies. The Varelsi bosses are much worse, the Maligner will get in close and drop in minions from the sky. If tentacles appear from the sky, jump to a different island. Long range Battleborn should attack from the opposite island, while short range should attack the enemies on the ground to keep things clear. The Gunhulk Varelsi can only be damaged by turning on the Voidbreaker turrets around the area, which get destroyed almost instantly by the enemies in the arena. Just keep running around the area and turning on the turrets until it whittles down the shields enough to make the Varelsi appear in the center of the area. It's now vulnerable and easy to take down. George Foreman Grill is powerful and capable of knocking you off platforms, so stay away from edges. Once his health goes down by a third or so he will shield himself and spawn black orbs. Destroy the orbs to take down the shield and keep attacking him. The last Varelsi will hover above the ground, dropping in minions and attacking from afar. Keep your distance and attack it hard, avoiding the minions on the ground.

After the boss rush, Rendain returns. He throws out these obnoxious spinning discs which knock you into the air, throwing you off the edges or repeatedly hitting you in a stunlock. If you or your partner goes down you'll probably be hit by the discs before you're able to get them up. Stay as far away from Rendain as possible with long distance Battleborn, if you're a close quarters character try to back yourself into a corner. After bringing down Rendain's health and killing him, you will unlock this.