Aren't owlbears pretty much the archetypical "A wizard did it" monster?
The owlbear description in the first-ever Monster Manual, includes the story that the first-ever owlbear was created by an insane wizard.
If I recall correctly, the owlbear is the only creature described as the creation of an *insane* wizard, though clearly many other monsters were first created by spellcasters.
A sane wizard can create a crawling claw or an iron golem. But only a MAD wizard can create an owlbear.
A crazy wizard named Ray, perhaps?
Meh. I think the insanity, intrinsic to the creation of an owlbear, is the waste of resources. Start with a bear, add an owl's head: how much have you increased the deadliness, compared to the normal, natural bear you started with? The one whose jaws and fangs can crack human femurs open, to get at the marrow?
A venomous bear, a flying bear, a spiky bear, a bear with a breath weapon or a gaze attack: nope. You put your magical efforts into making *a bear with better night vision*. Oh, and as a side effect, though it can't fly, it DOES inherit hollow, lightweight, fragile bones. Yes, Ray is crazy. It's kinda sad, really.