A decorative silver whistle that casts no shadow when held up to a light source. When blown, this whistle can summon a mysterious creature simply called a shadow wolf, a creature known to roam in packs in the realm of Shadowfell. These predators are adept at hunting at night and sneaking up on their prey, channeling magics to become one with the shadows to remain undetected. The juvenile wolf that resides in this whistle seems to have been somehow magically linked to the object in a way that allows some of it's unusual attributes to be bestowed upon the attuned user, if the wolf chooses to allow this. In order to summon this young wolf from the whistle, the attuned user must first give up a spell slot for the summoning. When the wolf appears, it will offer the following benefits:

Darkvision: While summoned, the wolf shares its powerful darkvision with its' handler.

Pack Senses: Once per long rest the user can mind meld with the shadow wolf. This allows the handler and wolf to communicate over any distance psychically, and to share senses. The two creatures can perceive everything that the other perceives. This effect lasts for 30 minutes.

Shadow Walk: Once per long rest the wolf can alter its physical form to appear as though it becomes a shadow. The wolf can move through narrow spaces as small as 3 inches in this form and gains advantage on stealth checks while in dim light or darkness. The shadow does not stretch or change shape based on light sources and this spell can be interrupted by a powerful light source. This effect lasts up to 3 minutes. 

Fungal Form: The shadow wolf has been impacted by the exposure to Mortharion's divine heart. He can use the spores within him to enter a fungal form, coating him in mushrooms and allowing him to grow larger. The wolf gains strength and becomes more capable in a combat situation. The shadow wolf will now use a new stat block which gives it new attacks, more hp, more resistance, and more. (Fungal Form Kyle)