The “Heart of Wormtail” collectible reward is awarded upon collecting Faded Wood Spirit, Faded Water Spirit, Faded Earth Spirit and finally Heart of Wormtail itself. It provides MaxHP +15 but more importantly unlocks a question box in your Adventure Handbook’s Collectible section.
Unlock Heart of Wormtail
First head to Prontera North. There you will find 3 Golden Stars on your mini-map. Head to each star to speak to the 3 Spirit Guardians. They will each give you a quest and upon completion will provide you the 3 Faded Spirits. Once you have all 3 rewards you will be provided one last task, finish that and you’ll receive the Heart of Wormtail. Open your inventory and deposit your reward into your handbook to unlock your reward.