The Gauntlet of Shar in Baldur's Gate 3 consists of three unique trials, which you must overcome to descend into the depths of the temple and confront the Nightsong. To drive a knife into the heart of Ketheric Thurm's immortality, you'll need to collect four Umbral Gems - three of which come from experiments, while the fourth Umbral Gem was stolen by Orthon who has a history with everyone's favorite demon, Raphael.
Once you've locked or fumbled your way through the shrine and entrance, you'll discover a central elevator that leads to a central platform that's missing its gems. Left the bank to find a waypoint for the temple itself.
Before going down the stairs, it is worth turning left from the waypoint and meeting the necromancer Balthazar. Although he's not a bright talker, chatting with him has the chance to glimpse a bell, which you can later use to summon a undead monster to help you in combat. Return to the waypoint, then go down the stairs to start the Gauntlet of Shar. Here's everything you need to know about it.
The Soft-Step Experience is a small labyrinth guarded by Shadows. You'll need to scramble to the end of the maze without being spotted, so send a stealthy member of your party. If you have an Enhance Ability spell available, it's useful to use Owl's Wisdom on them to help them spot traps.
Alternatively, if you don't have a rogue, Invisibility will do just fine. I'd recommend going into turn-based mode for this, though, as the Invisibility spell only lasts for 10 turns, which goes a lot faster outside of combat.
Head through the middle entrance, then turn right. Pull the lever to move two walls, revealing a hidden room containing a table with a Soft-Step switch (as with all items, you can hold down ALT on your keyboard to find it easier). If you want to skip the key, you can also choose to lock the door it opens.
Get the key, then go towards the end, avoiding both traps and wandering shadows. Ignore the entrance with a locked door - the key does not work on it - and go to the large gate at the end of the trial. If you are teleported back to the beginning, you don't have to pick the key back up again.
Alternatively, if you have access to a Dimension Door spell, you can bypass the trial entirely. The leftmost doorway gives you just enough line of sight to cast the spell through the window. Have the user teleport themselves and someone with Thief's Tools Mastery at the end of the puzzle, then choose the final portal. Claim your Umbral Gem and move on to the next trial.
You are your own worst enemy — literally in this case. Self-experience forces you to compete in the mirror with your party. To get to it, head down the same corridor and turn left. Before you interact with the bowl, be naked. It will help, trust me.
The experience creates copies of your party, dressed in whatever you've equipped. If you were naked before going into battle, they'd be naked too. You can re-equip your gear before entering combat, which seems unfair, but Ms. Char would probably approve of these sneaky tactics.
If you have the means to see invisibility, then it's worth preparing for this battle, as your clones will be able to dive in and get out of the shadows. Even without clothing, this can lead to a fight going on for longer than it should.
During the fight itself, both of you will be marked with a Mirror Trial. This buff gives a Stacking Curse that reduces each result of your ability points by 1 every time you hit someone else's mirror. However, killing a clone removes the debuff's real party member, allowing him to properly join the fight.
Before you catch and bounce the Umbral Gem, be sure to pick up the Killer's Sweetheart Ring. This bit is nearly perfect for Paladins, Barbarians, and Rogues, allowing them to count cash on demand once per extended rest period.
Third gem: The Faith-Step Trial
The Faith-Step Trial is the latest head-to-head challenge for the gauntlet. To find it, go downstairs and head through the first door you see. He donated a pound of meat to Mrs. Char in the ritual pot, as was customary.
The room will plunge into darkness. Before you do anything else, take a quick detour to the Options menu and turn up your brightness. There are platforms here, but they disappear the closer you get to them, requiring you to memorize the path. I would recommend taking a screenshot or even better using the image I provided above.
If you have access to the Dimension Door, I have good news for you: you can use it in this experiment, too. While the stone platform at the end is shrouded in magical darkness, you can still target one of the other invisible passages. From there, it's just a matter of hopping on.
If you have the means to jump or fly - like there's a barbarian in your party - you can simply jump across the stone platforms with the Lady Char statue on them. Make sure you climb into the unseen passages first, as jumping straight out of the ritual pot will send you right back up.
Sail through the void, stare into the abyss, and you'll be able to claim the next Umbrella Gem.
The fourth jewel: the Orthon



The fourth Umbral Gem can be found in Orthon's lair, and it can easily be missed the first time. Return to the Gauntlet of Shar waypoint, and turn right. Jump down the broken stairs and head down further until you reach a large room full of corpses.
If you simply enter the room, you will be ambushed by Orthon and her henchmen. This creature is an old enemy of Raphael, and killing it will earn him good fortune and advance your story with him and Astarion.
Fortunately, if you have a silver tongue, you can avoid this fight entirely by getting him to kill his minions, banter his monster, and then kill himself. The difficulty of these checks is rather high, so I would recommend Enhance Ability (Eagle's Splendor) on whoever speaks.
Then it's just a matter of keeping him talking about his binding contract here until you open up a check of persuasion to get him to slaughter his audience. Things pile up from there, and with a little luck, you'll leave the room full of corpses without even lifting a finger.
Whether you spar with Orthon, ambush him, or tell him to die by his own hand, you'll be able to pick up the Umbral Gem on the stairs next to her throne.
With that said, you'll have everything you need to go and fight Nightsong. Be sure to pay a visit to the Silent Library before you leave, though doing so is vital to Shadowheart's quest deck.