My headcanon for Lucifer Magne’s personality in Hazbin Hotel is basically a sillier and more childish version of Red Death from The Venture Bros.
(This dude: https://youtu.be/fKFVoMK4-os)
Normally kind, whimsical, and some what cordial but can easily switch over to being the single most terrifying individual you’ve ever met in your entire life, sometimes right on the spot.