Fantastical animals are not literally patchwork hybrids

I have already said my piece about the illogical and inconsistent treatment of fictional animals in fantasy gaming and the lack of consistent criteria for determining what constitutes a beast or monstrosity. In this post, I will explain the place of real and fictional animals (or beasts in the D&D rules) within my cosmology.

Retyping monstrosities

The inconsistent world building and rules in D&D drives me insane. I finally sat down and took a look at the fifty monstrosities in the MM and changed their type to something that is not literally a miscellaneous category. I included a commentary explaining my decision and, where applicable, the monsters' type in 4e D&D.

Beasts versus monstrosities, part deux

In past posts I explained my disagreement with the questionable logic behind the "beast" and "monstrosity" types. In this post I will explain some possible alternatives in greater detail.

What is a "monster"?

The word "monster" (with or without a capital M) has any number of definitions in the context of fantasy roleplaying games:

Beasts versus monstrosities

Many tabletop games treat magic as separate and self-contained from the "normal" physics of fantasyland. I believe that settings may be enriched by removing such arbitrary distinctions, hence my introduction of magical background fields underpinning reality. Continuing that line of thought, I would tackle the magic versus mundane argument as it applies to animals.
UPDATED 10/20/2017

Mundane versus magical beasts

Fantasy often makes a distinction between mundane and magical or supernatural beasts, which is often arbitrary and illogical. This distinction doesn't exist in 13th Age, which relegates all such things to Beasts. However, this sort of thinking still permeates the fluff to a much lesser degree. For example, the druid's beast form power states "Stick to four-legged natural predators, not creatures with supernatural abilities or the ability to fly." One of the listed aspects is the owlbear, which in other fantasy (outside Avatar: The Last Airbender) is considered a magical or supernatural creature. (The form itself is cosmetic, so even if this was ignored the druid still couldn't fly as a bird or petrify with a gaze as a basilisk.) How could this be explained from an in-character point of view without sounding silly?