Source: Van Richten's Guide to Ravenloft

Wondrous item, uncommon (requires attunement)

A dire wolf tooth dangles from this simple cord necklace. While you wear it, the necklace grants you a +1 bonus to ability checks and saving throws.

Curse. Attuning to Harkon's Bite curses you until either Harkon Lukas removes the necklace from you or you are targeted by a Remove Curse spell or similar magic. As long as you remain cursed, you cannot remove the necklace.

Upon donning or removing the necklace, whether you are attuned to it or not, you are afflicted with werewolf lycanthropy as detailed in the Monster Manual. The curse lasts until the dawn after the next full moon. If you are still wearing the necklace at this time, you are afflicted with lycanthropy again.