Just random things I thought of while messing about in creative. Listed in approximate order of how useful I think they are.

• Option for the player nametag to render even when morphed.

• Morph flight speed configurable separate from walk speed.

• Hovering in the air draining the player's hunger, like sprinting. (I assume actual horizontal flying already does this, since it's basically walking/sprinting?)

• An option for a morph to only display its arm when performing a block interaction animation, with the arm ducking out of view at other times. This would be useful for quadrupedal mobs like cats that use all their limbs when walking/standing, but could still feasibly use a limb for stuff.

• Perhaps the option for flying/hovering to drain the player's hunger faster than sprinting, or at a configurable rate per morph - this would help balancing against expensive late-game flight options, and also allow for some morphs' flight to be "better" than others (ex. a ghast has more flight stamina than a parrot)

• The option for a morph to be unable to hover - so if the user isn't pressing WASD, they begin to sink. This would provide more ''''''realistic''''''', less creative-feeling flight for larger flying mobs which you wouldn't expect to be able to hover in one place. Instead of hovering, the player would have to circle to remain airborn, like a large bird, and also take off at an angle (almost like a short run-up) due to the arrow key pressing requirement, rather than just ascending vertically.

• The above, but holding space still allows you to ascend without holding arrow keys (so you can 'hover' manually.)

• Separately-configurable ascent-speed per morph, for use in combination with the above.

• Morphs with 'sit' poses (cats, parrots, wolves) assuming their sitting pose when riding another entity.

And this one is kind of in a separate category, so:

• The ability to use player-specific textures for morphs. Ex: you add your customized spider texture to a folder, so whenever you morph into a spider you get that texture instead of the normal spider texture (a replacement of the default, not an additional option.) In multiplayer this would only be visible to you, of course, unless you shared the texture with friends. I imagine the player-specificity would be done through something like adding _(player's username) to the end of the texture name.