In Monster vs. Monster combat, two Monsters engage in combat until one is killed. Although uncommonly seen, monster vs. monster combat can be observed in a few specific locations. Some of the locations where Monster vs. Monster combat occurs are:
- Dwarf Cannon quest (goblins attacking dwarves)
- God Wars Dungeon
- Goblin Village (Red armoured goblins attacking green armoured goblins)
- Fremennik Isles
- Ratcatchers quest where Pox attacks rats.
- Ritual of the Mahjarrat quest final fight, temple knight vs Khazard, temple knight and Zarosian Mahjarrats vs Lucien and Zamorakian Mahjarrats.
- Khazard Battlefield (Khazard guards attacking gnomes)
- Ourania Cave
- The Lord of Vampyrium quest; first two parts of the final battle, the Myreque vs Lord Drakan.
- Rellekka Hunter Area Dungeon
- Land of Snow (2007 Christmas Event)
- Isafdar (Elves killing an Elf)
- Dorgeshuun quest series
- Chaos Dwarf Battlefield
- Zanik fighting monsters such as H.A.M. followers, Sigmund and the Bandos avatar
- Blood Runs Deep (Fremennik warriors attacking dagannoths)
- Summoning familiars and other NPCs allied with the player fighting other monsters.
During Gnomecopter trips (now removed from the game), player spoofs (e.g. Cow1337killr) in member-only areas are actually considered monsters, as they have unique examine options. In RuneScape one may notice that certain monsters, such as revenants, although designed to replace player killers, do NOT actually fight amongst themselves.
Monster vs. monster combat is sometimes used to an advantage by players because if they deal at least one damage, they will get the drops even though the monster dealt more damage. This is somewhat common in the God Wars Dungeon.