The Balrog in FOTR block faces 2 problems too often: skirmish cancelling and 
Armor / 
Gimli's Helm. To counter skirmish cancelling events you can pack 2x+ 
Relentless, but that's useful for 
Flame of Udun only since 
Durin's Bane fights by himself; also, that's only for events, so does nothing against 
Filibert Bolger and 
Gandalf's Staff. Instead, he can rely on 
Saruman's Snows to assure the skirmish will end in wounds or death.
To counter 
Armor and 
Gimli's Helm, you can use the 
Whip of Many Thongs at site 5, or 
Beyond the Height of Men / 
Isengard Smith at previous sites. But 
Saruman's Snows blocks your whip, and since requires to exert an 
![Isengard [Isengard]](https://lotrtcgdb.com/forums/Smileys/classic/isengard.png)
 minion the 
![Isengard [Isengard]](https://lotrtcgdb.com/forums/Smileys/classic/isengard.png)
 tricks will be better.
To increase the Balrog's strength, besides weapons, you can pack 4x 
Dark Places in a deck with very good cycling. To reduce strength on FP characters, 
Goblin Scrabbler can get rid of those irksome Last Alliances while 
Isengard Smith can do so with weapons. 
Goblin Warrior can deal with Thrarin (he also removes 
Endurance of Dwarves' tanking). 
Horn of Boromir can be a big problem though, and the only efficient ways to remove him I know are 2x+ 
Frenzy (with bulky Goblins, unique ones with 
Dark Places or 
Moria Axe are very good for such task) and 
Saruman SotE (with a strong, preferrably fierce dmg+1 
![Isengard [Isengard]](https://lotrtcgdb.com/forums/Smileys/classic/isengard.png)
 minion), also at a different site than 
Durin's Bane's.
That's if you want to build your deck around The Balrog. But if you just want to splash him, forget all I said above; 
Durin's Bane is awesome in 
![Sauron [Sauron]](https://lotrtcgdb.com/forums/Smileys/classic/sauron.png)
 grind or 
![Isengard [Isengard]](https://lotrtcgdb.com/forums/Smileys/classic/isengard.png)
 weather decks. He can also be great in corruption decks, 2x copies of him with 4x 
Must Do Without Hope and the highest cycling possible.