that shadow man is called the follower, on the main game to summon it you need to eat the buck to summon him, the closer they are a music called "the shadow beckons" will be heared but if you touch the follower it kills you, hope this helps.
HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT HFJONE I SEE HFJONE I EAT Im mentally insane
A little fun fact about me so if you see this on10hp please read this comment because I wanted to tell you that I also like the teapot floor whatever it's called