Ankous in OSRS are weak to all combat styles , so you can use melee, ranged, or magic effectively. A lot of players still prefer melee or cannon- based setups for speed, and the Salve amulet also works because ankous are undead.

Practical picks

  • Melee: solid and simple, especially for Slayer tasks.
  • Ranged: works well if you want safer distance or safespotting.
  • Magic: also viable; burst/barrage setups can work in multi areas like Catacombs.

Quick note

If you just want the most efficient answer: use whichever style you have the best gear for, since ankous do not have a strong elemental or style-specific weakness in the sources I found.

TL;DR: No specific spell weakness — ankous are generally weak to all combat styles, and magic is fine if that’s your best setup.