From a distance it looks like an enormous fox. From a distance it looks like an enormous crow. Close up it is obviously neither. It is a thing trying to be a couple things. Its skin is fluid and ink. When it moves it sort of...shapes itself in that direction. Stretching and blurring. It draws itself up like a man in a great cloak with the head of two beasts and walks overgrown trails. It is lightning quick and ascends like a black raindrop. He alights on a thin branch too frail to support a normal bird. He flies faster than an arrow, and sometimes vanishes altogether. He always comes back.
He is guilesome and condescending but he is aggressively sociable. He hunts companionship and feeds quite literally on confusion.
An extradimensional entity from the extradimensional playbook, "the foxcrow" is a classic manipulator. Honey-voiced and always waiting to pop up when the players seem like they're getting a handle on something, or at their most exasperated. In game terms he does NOT have powerful AC and he begins play with only 1HD worth of HP, minimum 4. He can teleport once per day and can, at will, alter self, charm person, fly 120', and cast phantasmal force. He can also cause any person around him to appear to be the foxcrow. However, every time his deception causes pain - every time someone takes illusory damage from phantasmal force or every time someone under his influence hurts themselves or another creature, he gains 4HP/1HD of hit points. He has one final ability, a floating 2nd level spell slot, which he may fill with any spell levels 1-2.
So long as a creature is aware of his existence, he can exist. Unless he is killed with a manmade (read: handmade) weapon he will always return to life within 1 hour. So long as a creature is aware he can come back, he can ALWAYS come back.
The fact that this guy didn't kill my players (YET) shows the value of a few well-placed bad rolls on my part and a ton of caution and nervousness on their part. That's partly engendered in presentation. You make it clear early that this is a threat, this is beyond you, this knows more than you, this is faster than you, and older, and everyone around considers him dangerous, and it doesn't play by the rules of a conventional monster.
That takes a few plates spinning to accomplish but it broods both a dread and a hate for the villain that a high AC, pile of HP, or beaucoup high level spells don't do on their own. It gives his demise a sense of accomplishment, the kind where my players are pretty sure he was the cause of all the problems on this godforsaken island, rather than A problem, and a symptom of a wider problem.
Low level magic, ambush tactics, and being a dick can be effective at higher levels, but when your party is only barely level 3 then we're a few initiative rolls away from a couple players going down and somebody dying for real. Keep your balors and stuff your Orcus, I can get by just fine with foxcrow.