Diablo 4 season 5 PTR patch notes reveal a new endgame roguelite mode and boss, new Uniques, and massive quality-of-life changes like re-playable bosses

gamesradar.com:

Diablo 4 season 5 is taking us back down to hell, as revealed in the wildly extensive patch notes for the new season's public test realm (PTR).

Though Diablo 4 season 5 has yet to be fully revealed, we learned about a ton of potential, and massive, changes in today's Campfire Chat and associated patch notes. I won't have time to cover every granular change, as again, there are a ton, but let's go over some highlights why don't we?

The twin headliners of the update are the new questline in which "enemies are cut-down, alliances shift, and unlikely friends emerge from the shadows," and the new and decidedly roguelitey endgame activity. The new questline takes place directly following the events of the main quest and will be available in the seasonal and Eternal realm, and will remain active on the Eternal realm even after season 5 ends. To access it, you'll want to head to Hawezar in World Tier 3 to look into a mysterious disturbance. 

Completing this questline will grant access to the Infernal Hordes, the new endgame activity that's a lot like Nightmare Dungeons but in Hell. Infernal Hordes tasks you with enduring "seemingly endless" and increasingly difficult 90-second waves of Hellspawn while collecting Burning Aether to unlock new gear, provided you survive 

You'll be able to access Infernal Hordes by using a Compass that grants access to Hell, not dissimilar to the Sigils you use for Nightmare Dungeons. Compasses have eight different tiers that scale in difficulty and World Tier; the higher tier the compass, the tougher the waves will be and, naturally, the more powerful the rewards. You'll also be able to upgrade Compasses while progressing using a new consumable called Abyssal Scrolls.

If you manage to survive all waves of the Infernal Hordes, you'll face off against the Fell Council await, which you might remember as a group of good guys in Diablo 2 but which is now very much a group of bad guys. There are five of them, but you'll fight a randomized selection