The Grim Dawn forum has been updated with 'Grim Misadventure #99' that lays out the first details about the game's survival mode called The Crucible. Originally a KickStarter stretch goal, the team wanted to deliver more than just players taking on increasingly difficult waves of monsters.
There will be several Crucible arenas that feature 150 waves of monsters in any one of three difficulty levels. The longer a player survives, the greater rewards can be earned. Death is, however, permanent. Every 10 levels, players will have to choose to go on for another 10 rounds for better rewards against even harder monsters, or to take the Tribute and run. Dying mid-challenge will reduce treasure "substantially", according to the post.
Tribute is the Crucible currency that can be used to purchase Celestial Blessings, Defenses or to gamble for better rewards.
And if that is not enough, monsters and / or players will feature Mutators that greatly enhance one global effect but significantly reduces another.
Examples of Mutators:
Berserking: Monsters are berserking, Attacking faster but also becoming more Susceptible to Attacks.
Slowed: Player Movement Speed is greatly reduced, but Crowd Control doesn't last as long.
You can read all of the details on the Grim Dawn forum.