The conquest Curses! and Stars Align requires you to "Kill 350 or more monsters in a Cursed Chest event on Torment X" in normal or hardcore mode, where Stars Align can be completed in hardcore only. These conquests can seem daunting, but are actually pretty easy to complete with the right setup.
Most classes with strong AoE builds are able to complete this solo, but UE and M6 Demons Hunters and wol monks are the easiest. These can clear this without any special gear, and probably only need around paragon level 200-300.
If you lack strong AoE, use the achievement hunter or conquest communities to find a group to complete it. It's extremely easy with a full four player group, and if you want to be 100 % sure to get it, invite at least one Demon Hunter to the group.
The hard part is however to get a Cursed Chest which is capable to spawning over 350 mobs. There is only one possibility in the game, namely the "The Cursed Peat" in Paths of the Drowned in act 5. This Cursed Chest is exteremly rare, so expect to spend between 30 minutes and 1 hour in order to look for it. The fastest way to find it is by constantly creating new games until you get The Cursed Peatbounty in Paths of the Drowned in act 5. Creating a new game to check for this event should only take 15-20 seconds each, but the bounty is very rare, so you need to create a lot of games.
Once you get the bounty, invite three people and clear the area. Once you click one the chest the timer begins, and make sure to start the area damage at once.