Karil's set effect: Karil's Taint, allows his hits to have a chance to reduce the player's magic level. When this effect is activated an animation and sound effect are triggered, and the player will suffer a loss of a magic level. This effect is not very damaging to a player if they are not using magic, particularly if Overloads are used. Regardless, his hits are rather accurate so protection prayers/curses are advised. Soul split can also be used, but should only be utilised by experienced players.
During the Morytania-Misthalin wars, the Barrows brothers were devastating the Undead armies, cutting through their lines with ease. Karil was known for his secrecy and accuracy in battle; "Should any enemy manage to survive long enough, and have the chance to strike a blow, Karil would fire a swathe of bolts to pepper their chest as they took their swing, throwing them back" (this is a quote taken from The Fall of Six under the Lores section of RuneScape).
Karil's crypt is located in the lower south end of the Barrows area. He's weak to stab attacks, but is also rather weak to melee styles in general, therefore it is recommended to use a strong weapon such as a Zamorakian spear, chaotic rapier or drygore rapier in conjunction with their off-hand variants. However other weapons such as the chaotic maul can also take down Karil just as easily.
It is common for many players attempting to slay the Barrows brothers to kill him with magic as it saves having to bring another combat style, however if this is the case caution should be taken when fighting Karil as he will deal heavier damage to mages than to melee fighters.
Karil does not have any drops, as rewards are collected in the chest at the centre of the Barrows, apart from the rare possibility of dropping a piece of Ghost hunter equipment.
Karil returns with his 5 brothers in Barrows - Rise of the Six, greatly enhanced by Sliske's experiments into the Shadow Realm. As when fought normally, he retains his set effect, and also has various other abilities. He has a special attack called Shadow Dash where he will dash into the shadows leaving behind Shadow portals in the process. If a player enters the portal, they will take 500 damage and be sent to the other side of the arena. If no one enters the portal, it will explode and can deal up to 8000 damage depending on how close the player was to the portal. He also has a special attack called Rolling Thunder, where he will send a line of lightning across the arena, dealing heavy damage if the player doesn't move away.
Karil, along with his brothers, appeared in Sliske's Endgame, being the second intended wave in Sliske's attempts to destroy the World Guardian. However, the Barrows Brothers had managed to regain a modicum of control over their own actions, and chose to aid the World Guardian, attacking Sliske's wights and champions.
Karil, along with all the other Barrows Brothers, received a graphical update on 4 January 2012 to make him look more like a player wearing his items rather than the old graphics style which displayed an unclear, purely pink coloured apparition. Along with this, his combat level was increased from 98 to 121. Due to the Evolution of Combat, his combat level has been raised to 150.
Although Karil uses range, he can do more damage to players with melee armour than Ahrim can, even though Ahrim uses battle magic. This is because Ahrim also uses his high-level curse spells on the player and occasionally uses his Fire Wave, unlike Karil, who just has a basic ranged attack.
Despite being a ranger and using his own armour (which would have high magic defence), before the Evolution of Combat, he could be hit extremely often with magic attacks. This would suggest that he would have a low magic level, or may be an oversight from Jagex.
Before a hidden update that affected Karil's and Torag's sets, Karil drained Agility levels from the player.
Karil's crossbow seems to be based off the real life Chu-ke nu, an ancient Chinese crossbow that used a rapid fire system. If this is true, this could also explain why Ak-Haranu sells the required bolt racks, as he is from the Eastern Lands and the Eastern Lands seem to be based on the ancient/medieval Far East. This supports the idea that Sliske, who gave the Barrow Brothers their armour, obtained them from the Eastern Lands.
In "The Fall of Six", Karil is depicted as being the fastest of the brothers, though due to the Evolution of Combat update his crossbow is not as fast as other crossbows.
In the wallpaper, Karil, along with Guthan and Ahrim, hold their weapons in one hand although all Barrows weapons are two-handed.
In Rise of the Six, Karil uses his regular crossbow, however, he holds it in one hand when running. When attacking, he uses the same animation for a two-handed crossbow.
Unlike the other brothers, Karil does not give bonus experience when killed with Ghost hunter armour.