'The Beyond' is the achievement for beating the extra, sixth Judge. You will need to unlock chaos mode. Here are the steps:
1. Beat the main game by defeating Kriterion in The Old World (Realm V).
2. Deny Kriterion’s judgement.
3. Press ‘continue.’ At The Chiming Tree (home base), run left to the skill tree altar. Scroll up to see the new skill ‘Truth Seeker’ available for 35 judge blood. You may need to farm a few more mini-bosses, judges, and blessings.
4. Make sure you also have the skill ‘Ground Pound.’
5. At the very left of the Chiming Tree, use ground pound (jump, then RB + down) to dive into the water.
6. Swim to the portal to see the ‘Roots of Chaos.’ Double-check the very top diamond says '6- The Truth' then press B to start the ordeal. You will now run through the main game again, but after beating Kriterion there will be a sixth, space-y world.
7. Realm VI's Judge is Endmonger, the Preyer of Worlds. He has several spam attacks that leave very few safe spaces on the screen. Save up your Fury before the fight so that you have at least one chance to clear projectiles. The biggest pain is going to be the environmental hazards around the room. You may want to lower the game and projectile speeds so you have time to maneuver. (And remember, Invulnerability mode guarantees a win here--or at the very least can let you practice.)
After the battle, Option A grants 'The New Vessel' and Option B grants 'The End of the Cycle.'
***NOTE: As of 26 Oct 2020, 'Invulnerability' does not actually disable achievements in ScourgeBringer! Go to ‘Accessibility’ in the options menu and change HP regen assist. This may be patched out later.***