Hickory: Ring/potion of Freedom.

If you don't want any of your party to turn on you as ghouls, you must have some dispel arrows/spells/scrolls, because the Tanar'ri casts death gaze regularly, and any member stricken will slowly die, then turn into a ghoul. If you see them dying, dispel is your only hope -- potions don't work.

Tactics: you MUST concentrate on the head disciple first, because she's a spellcaster who will cause you grief, then concentrate on the remaining disciples -- ignore the Tanar'ri for now; do not bother with buffs, because the Tanar'ri also dispel those; summon, summon, summon, to keep the Tanar'ri busy while you deal with the disciples; when the last disciple is dead, concentrate on the demon. All of this is because when you kill it, the demon jumps into any live disciple.

Elmofongo: Tell me is the final boss of the main quest harder than this Demon of the Dagger, my fighter protaginist Argronok is level 8 and has plate mail+3, long sword+2, etc.

Hickory: The fight can be harder because he has insane HP and hits really hard, plus his aides are not immobile, and will cause you all sorts of problems, and there are traps that cannot be removed. Be certain to take protection from fire items (ring, potions, scrolls, spells). And again, summons, summons, summons.

Coelocanth: What shows up is partly random and partly based on your level. You may get Ogres, Gnolls, Orcs, Dire Wolves, etc. No, you can't train them (they only last a short time anyway). But they're basically just there as cannon fodder distractions. They give you the opportunity to pelt the big bad with ranged attacks and/or spells. Don't be too worried about how powerful or weak they are. They're still incredibly useful.

Elmofongo: ....I did not take the summon advice, because I don't know if it works aswell as it should, for example:

1. What kind of creature can I summon a Wyvern, a Basilisk?

2. How strong will they be, do I have to train them or something?

Hickory: You have a cleric, so Animate Dead is incredibly useful because the summons last until they are destroyed or are turned (and they won't be turned in this battle), and they are completely immune to mind affecting spells, unlike most other summons. They are only meant to be fodder, so it doesn't matter how strong they are; just have your cleric memorise as many slots as possible.

Elmofongo: I am this close to beating the game:

I am trying to find the Underceller in the sewers, which sewer do I have to take the one in North Baldur's Gate, South, Southwest etc.

Hickory: Go to the Blushing Mermaid, in the back room.

Elmofongo: Forgive me but I am already at the UnderCity, so now there is nothing standing in my way to defeat Sarevok once nd for all.

Is he harder than the SuperBosses of The Tales of the Sword Coast expansion?

Hickory: You already asked this, and it was answered. Look up the list a bit... ^^

Elmofongo: OK the DemonKnight.......Strategic Recomendations?

Elmofongo: ...Or I could just buff the fuck out of my main character with potions again who is already incredibly powerful and kill Sarevok......and I just beaten Baldur's Gate 1 :)

levelworm: One tip: Protection from fire. BTW he casts Dispel Magic as soon as he sees you.
levelworm: Are you going to play BG2?