The dragon mace has a specal attack called "shatter" it uses 25% of the special attack bar and hits harder but less accurately than its auto-attack. This spec has the potential to hit massive damage but often hits 0's.
This can be obtained from Zeke for the price of 50,000 gp. Zeke is an npc that sells dragon weapons. He is located in multible places throughout soulsplit but most conviently just south west of the center of Varrock Square. (just south of the makeover mage)