Nine-Storied Pagoda
The Shadow Panther was a being that was made for assassination. It was half in the illusory realm, and half in reality.
One could hardly tell that it was there if they weren't paying enough attention. Even then, 95% of the people were never able to tell before it was too late.
The panther quietly melded into the shadows, remaining incorporeal and invisible from plain sight.
The Shadow Panther never acted unless it had certainty, and it didn't like to act against the strong ones. Instead, it liked to lurk around in the darkness and strike at the most opportune time.
Compared to most creatures and monsters, the Shadow Panther was smart and cunning, and it would run away when it thought that it no longer had a chance of winning, and it would not obstinately stalk its prey.
This particular Shadow Panther was currently following a group of four without any problems.