Agrith Naar attacks with melee or Magic. If the player uses Protect from Melee or Protect from Magic, he only uses the style the player is vulnerable to. If the player stands out of range and pray against his magic attacks, he doesn't advance to use melee and no damage would be taken. However, Agrith Naar would occasionally use a spell that looks like Telekinetic Grab which teleports the player right next to him.
He can be killed only with the use of Silverlight, which then is stained with ichor, becoming Darklight. As with all demons, he is weakened by the effects of Silverlight, and whilst fighting him, the final blow must be dealt with Silverlight. If the final blow is delivered to Agrith-Naar with a weapon other than Silverlight, he will regain exactly 95 life points. He is quite strong for his level and should be attempted with caution.
However, with a 50+ defence, magic and strength, it will be quite easy to defeat him if enough food like swordfish is available. Preferably a slash weapon like rune scimitar and full rune armour should be used if dragon is unavailable.
Agrith Naar likely came to Gielinor during the Second or Third Age, following Guthix's descent into slumber. According to Juna, Agrith Naar actively fought for Zamorak during the God Wars, ultimately forcing Guthix to banish him from Gielinor when the Fourth Age began. Still hoping to gain power in Gielinor, Agrith Naar found a loophole in his banishment, and managed to control natural disasters from within one of the Infernal Dimensions without being physically present in Gielinor.
According to Ellemar, a group of Saradominist priests faced off against Agrith Naar and brought him to the mortal realm, where they capsuled him into a human body. Even this was not enough to completely limit his power; during the Demon Slayer quest, Agrith Naar summons fellow demon Delrith under the guise of Denath inside Varrock.
In Shadow of the Storm, Agrith Naar is summoned by the player using the metaphysically weakened dimensional pocket beneath Uzer, where Thammaron entered the city during the Battle of Uzer between Years 3,000 and 4,000 of the Third Age. The demon has his own symbol, which is attached to the sigils used to summon him and is also on Denath's chest. It looks like two arrows pointing down, connected by a line at their tops. Agrith Naar is ultimately slain by the player, and his blood stains Silverlight, turning it into Darklight.
In this alternate realm, Agrith Naar and Delrith are not comrades, but enemies. Agrith Naar consistently picks on Delrith, which continually angers the latter as he does things such as "making it rain", which he hates.
When the adventurer goes to Delrith, who presumes them as another crazy cultist, when they hit them with Silverlight he sees a chance to escape back to Infernus. When the adventurer attacks him again, Agrith Naar uses a bolt of lightning to deflect their attack from hitting him, and Delrith presumes that he doesn't want the adventurer to kill them as he enjoys picking on him. Delrith guides the player through a blood ritual, and upon being stabbed with Silverlight and a proper ritual, returns to Infernus. He later confronts Agrith Naar and banishes him to New Varrock, which he mentions that he hates. Angry at the player, he attacks them but is ultimately slain by the player. As like the normal realm, his blood stains Silverlight and turns it into Darklight.