God Wars Dungeon
In the God Wars Dungeon, 40 followers of Saradomin, Zamorak, Armadyl, Bandos, or Zaros must be slain in order to reach their respective generals. The only exception to this is the Ancient Prison, in which players can opt to wear full ancient ceremonial robes to go straight to the banking area that leads to the lair of Nex, the Zarosian general. Though players can still choose to access Nex by killcount.
The killcount for a god will be reduced by 40 when entering the god's boss chamber. The rest is saved and can be used for subsequent entry. However, leaving the God Wars dungeon completely causes all killcounts to reset to zero. The generals and their bodyguards also count towards killcounts. The killcount interface in the top-right corner of the screen displays killcounts against the followers of the four gods represented in the dungeon.
The weakest followers of Saradomin that can be killed for the killcount are knights of Saradomin. Saradomin priests, Saradominist spiritual warriors, spiritual rangers and spiritual mages can also be killed for this purpose. Killing 40 of these grants access to Commander Zilyana and her bodyguards: Starlight, Growler and Bree.
The weakest followers of Zamorak that can be killed for the killcount are imps. Bloodveld, vampyres, hellhounds, werewolves, pyrefiends, icefiends, goraks, Zamorakian spiritual warriors, spiritual rangers and spiritual mages can also be killed for this purpose. Killing 40 of these grants access to K'ril Tsutsaroth and his bodyguards: Tstanon Karlak, Balfrug Kreeyath and Zakl'n Gritch.
The weakest followers of Bandos that can be killed for the killcount are goblins, specifically the level 120 variety. Ogres, jogres, hobgoblins, orks, cyclopes, Bandosian spiritual warriors, spiritual rangers and spiritual mages can also be killed for this purpose. Killing 40 of these grants access to General Graardor and his bodyguards: Sergeant Strongstack, Sergeant Steelwill and Sergeant Grimspike.
The weakest followers of Armadyl that can be killed for the killcount are aviansie, specifically the level 128 variety. Armadylean spiritual warriors, spiritual rangers and spiritual mages can also be killed for this purpose. Killing 40 of these grants access to Kree'arra and his bodyguards: Flight Kilisa, Wingman Skree and Flockleader Geerin.
The weakest followers of Zaros that can be killed for the killcount are blood reavers. Ancient warriors, ancient rangers and ancient mages can also be killed for this purpose. Killing 40 of these grants access to Nex and her bodyguards: Fumus, Umbra, Cruor and Glacies.
Heart of Gielinor
In the Heart of Gielinor, 40 followers of Seren, Zaros, Zamorak, or Sliske must be slain in order to reach their respective generals. However, this is reduced to 20 followers if the player has unlocked the reduced killcount perk from that faction. Unlike in the God Wars Dungeon, however, killcount is saved when leaving the area. The killcount cap at the Heart is 200 to compensate for the saved killcount. Like the original God Wars Dungeon, killcount is used to enter an instance, though no other fees are applied to the instance. The Heart of Gielinor also has a unique multiplier system where quick streaks of killing followers allows the player to earn multiple counts for killing a single follower. In addition, the generals themselves do not give any killcount. Having the God Insignia set to prevent damage to your chosen faction does not allow you to get a killcount for that faction in order to enter the boss areas. Set the Insignia to allow a killcount for that faction. Right click, toggle collection.
A killcount system is also used in the Barrows crypts. Killing any of the monsters in there (save the final brother) will add one killcount. The weakest monsters to kill are level 74 crypt rats, with the strongest being the level 84 giant crypt spiders.
The killcount in Barrows affects the drop rate and quantities of certain reward items.