Helm of the Hydra (2012)

From publisher blurb:

Legendary items are those that are picked up by the untested adventurers who eventually become heroes of the ages. Unlike traditional magical items, legendary items grow with the wielder, becoming more advanced as new abilities are unlocked over time. In this installment of the Psionic Items of Legend series is the Helm of the Hydra, which grants the wielder the ability to coordinate with allies and even join forms.

Within this short book you will find the history of the Helm of the Hydra, the requirements to attune a character to it, and the abilities of it. In addition, the rules of legendary items are detailed.