With Haunted Visions and Inarius' damage mitigation being buffed, Inarius-Generator is far easier to gear for than its LoD counterpart. While you may lack Stone Gauntlets, having a flat 90% damage mitigation once you find a Wisdom of Kalan really helps in Season 21.
When you enter a GR, DO NOT POP SIMULACRUM IMMEDIATELY. You have no cooldown on this build, so if you die with Simulacrum on cooldown, it's going to be a LONG wait to get it back up.
You're dependent on Final Service to keep you alive long enough to find a large enough pack to pop your Bone Armour to get your damage mitigation. With Razeth's, immediately use your Command Skeletons to drop your Essence below max to get the Razeth's triggered, remember to attack with Grim Scythe to apply a Curse. Hopefully this will get you a decent amount of Bone Armour stacks so that you can survive for the next 9 seconds to max out your stack count at 15. Once you're confident you can survive, use Simulacrum to triple your damage.
You have 5 Poison Skills and Simulacrum: Blood and Bone. You'll need to cycle through your 5 Poison Skills to keep up 500% bonus damage via your cubed Nayr's.
For a burst of damage, Cast all skills once -> Skeletal Mage -> Bone Armour: Dislocation. This allows you to refresh your Nayr stacks, empty your essence bar, then Stun the enemy to trigger Krysbin's 300% damage. The next few swipes with your Grim Scythe will deal a LOT of damage.
Note that you'll need to reposition yourself constantly. Look at your screen and make sure that your Simulacrums are actually hitting your enemy. In long, windy corridors, it's especially annoying when they're standing just behind a wall.Guardian's won't be a problem. They're usually big enough that the Simulacrums will be close enough to you that all 3 scythes will hit your enemy. Normal Elites and trash mobs are the problem.
Unlike the LoD version, you don't have the luxury of Illusory Boots, but this Necromancer is really tanky. Just be careful in long, narrow corridors where Arcane Enchanted/Waller enemies can really screw with you because you can't reposition yourself easily.