In Baldur's Gate 3, General Ketheric Thorm is introduced to players formally around the middle of Act 2, once traversal of the deeper Shadow Cursed lands becomes available. The invulnerable General of the Absolute isn't so tough once players rescue the Nightsong from the Shadowfell, cutting off his source of immortal powers.
After getting through Moonrise Towers' many True Souls and other enemies, players will find themselves face-to-face against a weakened Ketheric Thorm. But don't take this BG3 boss fight for granted – though the first phase is relatively easy, the second phase is one of the game's most difficult, yet cinematic, boss battles.
Phase One: Tips To Beat Ketheric Thorm
Use Turn Undead & AoE CC To Negate Necrolytes
During the first phase of the fight with Ketheric Thorm, the General will regularly summon Necrolytes to bolster the enemy roster. The Necrolytes aren't too much of a threat – not enough to draw away focus from Ketheric himself – but some AoE abilities that target Undead can be incredibly useful here.
The number one choice for any party should be Turn Undead, a Channel Divinity power available to Clerics. A Life Cleric can use Turn Undead in the middle of the battlefield atop Moonrise Towers to practically take away the Necrolytes from the fight, literally turning them away and dealing a huge amount of damage to each one.
Thorm will sometimes use Incubate Death to create new Necrolytes after a turn of growth. It can be worth taking out these growths to turn the Action Economy towards the player's party's favor, as the enemy team will have overall fewer turns for actions. In general, though, turn to AoE for the adds in the Ketheric Fight, and consider using spells that do extra damage or effects to Undead.
Keep The Nightsong Healthy & Buffed
The most important part of this fight is to keep the Nightsong alive. Dame Aylin is responsible for the vast majority of damage output in fights she takes part in, but despite her being the daughter of a Goddess, she can still be taken out of the battle if her immense HP drops to 0.
Keep a party member on support for the Ketheric Thorm boss fight, and make that party member focus on buffing and supporting Nightsong above other party members. You will find her to be a powerhouse of damage, able to nearly single-handedly take down Ketheric in a matter of turns with the right setup. However, Ketheric can't actually be killed in this first phase.
Focus Ketheric – The Tough Part Ends When He Reaches 40% HP
General Ketheric Thorm, now robbed of his invulnerability with the release of the Nightsong from the Shadowfell, is mortal. He can be hurt, and killed, but not finished in this first phase. Instead, once players bring him down to 40% HP (which changes depending on your difficulty mode), the fight will end with a cutscene.
This concludes the first phase of the Ketheric Thorm boss fight – after speaking with Jaheira and cleaning up the mess, jump into the bowels of Moonrise Towers to find the Mind Flayer Colony. Here, players can explore to finish a number of questlines, and learn the truth of the Absolute (if they haven't already) when they meet the three that control it.
This pivotal moment ends when Ketheric sacrifices himself to become the Apostle of Myrkul, an immensely powerful enemy, one shrouded by the God of Death, and the true final boss of Act 2.
Phase Two: Tips To Beat Apostle of Myrkul
Use The Restoration Pod Before The Elevator
Just before taking the elevator down to the boss room, where players watch the cutscene with Ketheric, Orin, and Gortash, there is a Restoration Pod to the elevator's right. These Restoration Pods work just like they did in the Baldur's Gate 3 tutorial aboard the Nautiloid. By interacting with one, the whole party will regain full HP and spell Slots, and lose most negative Status Effects.
The Restoration Pod can be used over and over again, so be sure to use it before exploring the Mind Flayer colony itself. There's a lot to do in the Mind Flayer Colony, and more than a few combat scenarios, so be sure to take advantage of this healing station in this intermission between Ketheric's first and second phases – and don't forget to save.
Free The Nightsong As Soon As Possible
When the fight against the Apostle of Myrkul boss begins, players see the Nightsong ensnared once again, in the back right of the room. The Apostle of Myrkul takes up the center of the room, but doesn't move. However, would-be rescuers should still watch out for the Necrolytes and Mind Flayers that occupy the room's outer areas.
The Apostle of Myrkul is invulnerable while the Nightsong is imprisoned, so characters not involved in her rescue should clear the path to her and CC other mobs as they advance towards the boss. The Nightsong is an immense source of damage, but it's the removal of the Apostle's invulnerability in phase two that makes her rescue such an imperative task.
The best way to do this is to make one of the party members invisible, preferably one with great movement abilities like Lae'Zel, or one that can remain stealthy while moving great distances like Astarion. Use the Dash action to double movement speed, but keep an eye on the remaining distance. When 3m movement speed remains, use the Jump action to get a little further than normal, or to get across gaps and ledges.
Use Concentration CC & AoE To Take Minions Out
The Apostle of Myrkul is an impressive foe, one that has a lot of minions to do its bidding all over the room – and one with the ability to create more allies on a whim. As such, though the Apostle of Myrkul should be your main priority, it can't be damaged until the Nightsong is freed once more. Until then, spend turns advancing toward the Apostle of Myrkul and using CC and AoE attacks on the boss' minions.
To the right and left of the Apostle's central location there are a few groups of enemies. Spells like Hunger of Hadar, Confusion, and Hypnotic Pattern go a long way in preventing these enemies from engaging in combat.
Forget Healing: Buff & Focus Down The Apostle Instead
The Apostle of Myrkul has a unique Aura called Bone Chill, which prevents healing in all forms including the Help action, which normally brings Downed allies back up with 1 HP. As such, casters should prepare buffing spells like Bless, Enlarge, and Freedom of Movement instead of spells that heal, alongside damaging spells of course. If a party member is looking worse for wear, move them away from combat and allies with the Disengage action and hope the Apostle's focus changes to someone with more HP.
After the Nightsong is freed, turn your attention towards the Apostle of Myrkul exclusively. Single-target melee abilities and spells are perfectly fine for th fight, but AoE spells like Cloud of Daggers and Moonbeam are extra-powerful. Spells like these will often deal damage multiple times in a single turn as the Apostle moves slightly back and forth, triggering the effect over and over. If the fight ends up feeling impossibly difficult, consider preparing some AoE damage spells like Cloud of Daggers beforehand.
When the boss dies, the fight ends, so go all-out on dealing as much damage as possible in a short amount of time once its invulnerability is removed. Some minions may escape their CC (remember to check for current Concentration spells before casting another), but with a party at around level 8 or 9, the fight should be over in a matter of two or three turns from the point that the Nightsong is freed.
Baldur's Gate 3 is available on PC and PlayStation 5. A version for Xbox Series X|S is currently in development.