Part I: Heart of Darkness

Go to Gloomwald and search for the house as shown in the screenshot below and open Nane's stash, in order to retrieve the note. Then go back to the northwest to take the secret passage as on the second screenshot. Take the chest then continue the path to find the blacksmith Acturus Cursed Smith. Then forge Heart of Darkness via this one.

Part II: Sahdina's Memento

This part is quite simple, go to Devil's Crusadering and click on the big beast dead on the ground, click several places on it until you find the amulet. Attention it is rare (green) so can go unnoticed in your inventory!

Part III: Mythical Stormheart

To collect the last item, go to Desolates Wastes, the rift accessible via the Rattosh Altar north of Barrowholm. Go all the way north and destroy the urn at the screenshot below. Be careful, she only drops once per character!

Part IV: Flameond Bleu

Be careful, this part is by far the most tedious. You need to go to Malmouth Outskirts south of the rift. Look for a little blue creep like on the screenshot, the Blue Flameond. Go first to locate the altar which is near the Shrine, but being careful not to kill the Flameond.

You will now have to bring it to the white circle. Remember to clean the surrounding creeps and deactivate all your retaliation and automatic cast spells, in order to avoid killing the beast. Once spotted, bring it without touching it to the circle. He will follow you without complaining as long as you don't stray too far! The Flameond has three spawn areas inside Malmouth Outskirts.

Position yourself as on the screenshot to make sure the Flameond goes through the circle, without you being too close to him.

You will then have an aetherial rift which will appear for the rest of the quest.

Part V: Rift of the Celestial

Give the objects to the spirit and take the rift. Behind the Shrine you can open the wall (be careful to stick well, you need a left click, not an attack) and start the rift. Be careful, it stings, lots of creep and invulnerable turrets / mobs that take pleasure in freezing you. Consider making portals while you can!

Once you have reached the river of blood, turn left into the secret passage. There is no point in going further on your right. Make a portal at this level (this is the last possible place) and continue under the 2nd secret passage.

You will have to kill the Root of All Evil plant boss, not super powerful but watch out for poison damage, then take the rift towards Lokaar. Remember to take your potions first!

Part VI: Celestial Lokarr Fight

You are not unworthy of getting there, but the ultimate effort will have to be made! To kill him if you can't resist his damage (like in the video), you can permanently kite him. Prioritize killing add-ons that can freeze you and send powerful projectiles into your head!

It has a lot of health and damage, so take your trouble to drop it. Don't forget the chests at the end, and with "a little luck" you will potentially have the Lokarr's spoil set which gives 40% once all four coins are together (yes it's not terrible, but the Celestials are here for the day). glory! ^^)