This is the hardest wave/achievement in the DLC. In order to obtain this achievement, you’ll have to complete the bonus wave (Wave 21) on the last arena (Arena 4), complete it on a public match to get the "Heretic" achievement too.
Note: If you fail on this wave you'll have to start all over again from Wave 16.
There is also a new enemy on this wave (Killa Kan) he’s like a big robot and he uses a machine guns, he will kill you in a few shots if you didn’t take cover but here are some of my tips, I hope that it will help you to beat this wave with the easiest way possible:
1. You should have all of your weapons unlocked or at least the important weapons + perks, and here are the best loadouts:
- Raptor: Daemon maul + Plasma pistol, Killing blow + Impenetrable.
- Raptor: Chain sword + Plasma pistol, Swordsman’s Zeal + (Impenetrable OR Sure Strike).
- Tactical: Melta gun + Daemon eye bolter, Weapon versatility + (Improved melta charge OR Stalker ammo reserves).
- Havoc: Lascannon, Ammunition stores + (Feel no pain OR Iron Halo).
2. At least 1 or 2 players must pick Raptor class and let the ammo for the others, because if you all picked Tactical/Havoc classes you will end up running out of ammo.
3. Priority of killing: Bomb Squigs > Shooters > Melee > Killa Kans.
4. Always stick together and cover each other back.
5. It's better to use Plasma gun/pistol and Melta gun against the Killa Kans, because it will do really heavy damage to them.