Does Rune Halberd have a special attack in RuneScape?

No. All halberds have the advantage over other weapons for its long reach, able to hit opponents two to three squares away. This could be useful when fighting stronger monsters from a distance so you don't get hit. Only the Dragon Halberd has the special attack (allows player to hit multiple enemies at once if they are in the correct spaces) and can also attack from a long range.