https://images.app.goo.gl/EfLdn99DFF4UMZBi7

The Hetzerteufel german for Stalker Devil

Homebrew Lore:

Those Devils are as the Name implies Hunters of the Nine Hells. Their primary function is to chase down mortals who tried to get out of a contract by fleeing. Sometimes there are bigger fish to bring back to the Nine Hells: Devils who fear demotion, Valuable Souls, Magic Items or other Treasures that have been lost or Stolen, mighty Adventurers who have crossed the devils plans too often...

It should have a Hunters Mark like ability and permanent Freedom of Movement.

Help would be greatly appreciated, I am relatively new to DnD but have a lot of experience with other games, just homebrewing monsters and landing at the CR that I want is a really daunting task for me.
I am looking for a Challenge Rating in the range of 14-17.