NPCs that fight each other
 

i.e. bixies vs orc pawns in ecommons

What are some others in classic?

The Monk guy in Qeynos and the Preist of Discord. Was always a good fight.

Edit: hes actually not in on this server. Idk why he isnt, but he isnt there.

Gargs and skellies in OOT.

Orcs and Citizens in High Pass

Brother Chintle and Trintle should fight, but I've never stuck around to see if they do or not.

Fippy versus all humans in Qeynos of course... but I'm trying to come up with something a little less lopsided.

This sounds entertaining - an old post on FOH forums:

"Oh, get a friend to help pull the paladin guild house and you will have the paladins and monks fighting it out. Those monks would curbstomp the paladins every time."

Wonder if this works on this server.

I always loved to watch orcs and mummies duke it out in North ro or the oasis.

There's the executioner's quest in Qeynos.