This article is a rough walkthrough of how to beat the Balrog as quickly as possible, with various methods. These are not failproof, but certainly speed up gameplay. When choosing between them, it is generally best to go with whichever required items are obtained first.
Required Items: 2+ Runes of XP, a Portal to Chaos
First, a good rule of thumb if you plan on this method is to return to the Overworld every three floors or so to drop off your strongest weapon and armor at that point, as well as one of each identified rune. This way, you gain rune identities as well as a store of weapons and armor. Once you get to Chaos, you must begin farming for Runes of XP, which you can locate there. Be sure to use a gnoll face when opening chests, as they provide a scavenging bonus.
The best place for the Overworld Portal in this scenario is one floor beneath the Balrog's spawning floor. This way you can die and restart multiple times until you are able to find a Rune of XP, and the Balrog will be nearby. This method truly takes advantage of the portal system and the ability to restart the game.
Once you have at least two Runes of XP, chase the Balrog until he is in a corner. He always moves toward the floor exit, so one way to corner him is to circumnavigate and come around to block his path. His inclination will be to move towards you. Next, eat the two Runes of XP consecutively to guarantee quickening him to death. Having your minion with you provides even more lightning, which is useful.
Required Items: 2 Bleed Runes, a ranged weapon or Rune of Holy
Bleed Runes drain just under half of a creature's health when thrown at them, so one simple method of defeating the Balrog is to throw two bleed runes at him, which will lower his health down to almost nothing. From there use a ranged weapon to pick him off, or a rune of holy to guarantee his death through the resulting explosion. This method is probably the simplest one to achieve, given that it only requires decent equipment and some common runes.
Required Items: A portal to the Underworld, a Nymph's form
Death has in his possession a Level 20 Scythe, by far the strongest melee weapon in the game. It is also enchanted heavily with Undead runes, meaning that it is less effective on Undead than you might like, but that it also heals the Minion with every kill, or revives the Minion if he has died.
The next step, becoming a nymph, is fairly difficult, but there are many ways to do it.
- Get a Mimic face and fight Nymphs to steal their form
- Polymorph yourself, get RNG to polymorph you, or get hit by a chaos rune that polymoprhs you into a Nymph
- Decapitate a Nymph and get its face
Once you have done this, open a portal to the Underworld by praying to RNG. Attack Death as a nymph and you will obtain his Scythe, which gives you a massive advantage over other monsters. You'll still have to get to the appropriate level, but since the Balrog is not an Undead, attacking him with the scythe is a fairly reliable way of killing him. It's still a tad bit unfair, but less so than the Quickening method.
Required Items: Lots of Stun Runes and/or a high-level blessed weapon
This is less fleshed-out than the rest, but basically the best way of preventing Balrog from jumping past you is being able to stun and knockback the Balrog. If you have high-level weapons that you cast Holy on to bless them, or just lots of Stun runes on them, they can effectively lock the Balrog in place and prevent him from descending to the next level.
Required Items: Rune of Polymorph or Werewolf form (rogue and/or minion)
Polymorphing the Balrog will transform him into a powerful regular enemy. This will often make him much easier to defeat, and is not too difficult. One way to do this is to cast a Rune of Polymorph on him, which can be found later on in the dungeons. It is a good idea to have a second one in case the Balrog is polymorphed into a different powerful monster.
Another way of doing this is via werewolf bite. To do this, have yourself and/or the minion polymorphed by a werewolf. Next, engage in a close-combat fight with the Balrog, and eventually he will turn into a werewolf. This will require you to have a high level or at least very good armor, so as to survive long enough to polymorph him. After this, killing him becomes far easier.
Required Items: Many monster heads
Monster's heads can do damage when enemies hit them, and it is no different for the Balrog.
To set this system up, get a bunch of decapitated monster heads on a level where Balrog already exists, but hasn't approached the bottom stairs yet. You'll want to kick the heads so they are all in Balrog's way as he approaches the bottom stairs. Be careful not to crush the heads!
At any rate, once you've set up this obstacle course, you just need to chase the Balrog and he'll run into the heads himself, greatly decreasing his health and potentially even dying just from that. If not, then you can finish him off.