Lasus Duskheart

A vampire spawn we met in the undercity of Praag. He made Kemurial, Freya, Lim Dul and Rory a deal that in return for allowing him to sample our life force (blood, obviously), he would grant us a powerful magic item. He assured us many times that the effects of his sample bite would only be temporary, and there would be zero lasting effects. Kemurial believed him, so all of us except Lim Dul took him up on his offer.

Kemurial received a Censer of Controlling Air Elementals. Freya received a Staff of Charming. And Rory received an Ioun Stone of Protection. The effects seemingly did, in fact, entirely diminish after a long rest.