Hexcrest

The hexcrest is a unique Slayer item that is dropped by Jungle Strykewyrms. When worn while slaying, it boosts the player's Magic damage by 12.5% and Magic accuracy by 12.5%.

Full slayer helmet
You can make full slayer helmet by using a hexcrest and a focus sight on a normal slayer helmet. They provide the same damage boost as hexcrest and focus sight combined giving the Full Slayer Helm a + 3 Range and + 3 Mage Attack Bonus. The dissasamble option also works on full slayer helm.

Trivia

 * The full slayer helm is one of the requirements for the PvM God title.
 * Players are not aware of the bonuses that the hexcrest may give you, when combining it with another item.
 * Hexcrest and Full Slayer Helms, are somewhat rarely seen on Soulsplit now, in retrospect of back in the days.