He seems to be wielding a damaged primal 2h sword and full primal armour. In order to kill him the fastest, players should use Bind or Entangle while killing the rest of the skeletons. Players should also use magic on him to take advantage of the combat triangle. Any of the Surge spells are the best choice for this skeleton. Wave spells aren't as effective but they still will eventually kill him. If players are unable to use Protect from Melee, DO NOT get in melee range, or players will use their food extremely fast. Still, it is recommended, that they kill the mage and archer first, because it is possible to block the warrior behind one of them.
Another strategy is a team member can also run around the room with the warrior on them, so then it is out of the way when the other 4 members of the team (assuming the large floor has 5 people) kill the mage and and archer, Also players can cast the spell Entangle on the warrior to keep it from moving whilst you deal with the ranger and archer. Keep in mind that the warrior will switch targets often, much like Commander Zilyana.
Despite the skeletal warrior wielding a primal 2h sword which requires 99 Attack, by using the curse Turmoil and attacking the skeletal warrior, no extra percentage boost is given to the Attack part of the curse and it is capped at its default percentage (15%). This means that the Attack level of the skeletal warrior is very low, most likely 1. However he is still capable of hitting 700+ but his attacks hit rarely, even on no armour if a player has high Defence. This is a glitch and has not yet been fixed.
Strangely, when the skeletal warrior switches to Protect from Melee, his combat level will rise. But when he switches prayer again, his combat level goes down.