USING:
Minecraft 1.12.2
Latest curse version of Morph for 1.12.2
ATLauncher
Custom mod pack (in development)

ISSUE 1:
When morphed into a bird (mocreatures) or any 1 block creature, any contact with the bottom of the block above the player causes damage/suffocation.

ISSUE 2:
When morphed into a non-player entity, the player sinks immediately if a certain depth of water is reached (for me typically 4 or 5 blocks deep), cannot resurface but bobs up and down rapidly. A similar occurrence happens midair with NPC Manticores (mocreatures), and NPC wraiths (mocreatures). Likely other flying overworld entities as well.

If modlist needed, I will provide. Around 100 mods is a pain in the ass to type out though.

Issue 1: Does the suffocation happen with Minecraft chickens and bats too? This normally happens because of mobs not setting the entity eye height properly.

Issue 2: I'm not too sure what's causing this. I don't know if I've had similar issues with just Morph installed. It potentially might be a mod conflict.

Unfortunately it's unlikely I'm gonna fix this cause I've ceased supporting my mods for 1.12.2. I'm busy IRL and my next focus for my mods would be to bring them over to newer versions eg 1.15 or 1.16.

Its fine if you can't fix it, I might have the time to sort through that but yes chickens and bats take damage as well.