He has a special attack where he uses a green magical attack that explodes and can deal high damage, similar to the Crazy Archaeologist's explosive book attack. Players must run away from them to avoid damage. He is also able to disarm players, much like how the Chaos Elemental does.
The fastest way to get there is by casting Ghorrock Teleport or using its magic tablet equivalent. Alternatively, a burning amulet can teleport players to the entrance of the Lava Maze; run west from there. Alternately, players with the hard Wilderness Diary completed and a POH obelisk can select the level 44 Wilderness teleport.
Quotes
One quote is said every time the Chaos Fanatic attacks the player.
"BURN!"
"WEUGH!"
"Devilish Oxen Roll!"
"All your wilderness are belong to them!"
"AhehHeheuhHhahueHuUEehEahAH"
"I shall call him squidgy and he shall be my squidgy!"
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Trivia
The Chaos Fanatic's animation (apart from attacking) is similar to Dr Harlow before he is sober.
The Chaos Fanatic's quote "I shall call him squidgy and he shall be my squidgy!" is a reference to the Pixar movie Finding Nemo.
The Chaos Fanatic's quote "All your wilderness are belong to them!" is a reference to the phrase "All your base are belong to us," which originated in the 1989 game Zero Wing and has made it into many games since then.
The Chaos Fanatic's quote "Devilish Oxen Roll!" is an anagram of "Lord Helix lives on!", in reference to Twitch Plays Pokémon.