I'll list some things that stand out to me in the trailer.
- The new affliction league mechanic opens a hole in the ground in your maps. You have limited light and you run out of light if you move too much. Not sure about this.
- There's a new item called a tincture. You can only use 1 tincture at a time. It functions like a flask and goes into the flask slot. This is maybe a nerf to mageblood belt.
- The league mechanic allows you to have a second ascendancy tree. It appears that this is not linked to your class and there 3 options in total, one of the ascendancies allows you to socket special items called charms.
- There is a new way to add mods to monsters, called wisps. Wisps make the monster stronger but also drop more loot. It will be interesting to see how these mods interact with other mods like nemesis mods, delirium mods, and tormented mods. Last league had an exploit where combining tormented and delirium monsters mods would cause an insane amount of loot to drop.
- The league mechanic includes a new itemized corpse which is purchased at a vendor. You can place the corpse on the ground. One of the new league ascendancies allows you to consume the corpse to have extra damage and survivability. You can also turn the corpse into a spectre minion, this could be a huge buff to minion builds.
- One of the league ascendancies includes 3 new curses, including one that causes monsters to explode. Explode is always good for clear speed.
- Ultimatum is going core. METAMORPH IS REMOVED FROM THE GAME Catalysts have been added to Ultimatum.
- Labyrinth Enchants and Alternative Quality Gems are REMOVED FROM THE GAME?? The Labyrinth now allows you to create a new type of gems called Transfigured Gem. This probably breaks a lot of builds but also makes new builds possible. This is a massive game change.