Prime Directive= Gameplay

Generally for games a creatures primary feature or function in terms of gameplay-

as a result the need to communicate the idea or meaning of the character or creature, as a game piece, and the need to be able to see and understand what things are and what they do can take precedence over  the reality of a creature or person (if it were real). That said any fantasy elements of modifications to common sense you make should be self consistent in their fantasy logic- otherwise confusion and frustration and lack of immersion is the result.

ie attack or special attack- as a mode of transport- as a prey animal or something to collect, and the way you communicate what that feature is dictate the look of a creature.

In games you are what you do- so often the trick is conveying to the player what something does- and how that piece fits into the game or how it should work in terms of gameplay is a goal to keep in mind.