The model used for drowned mobs has some issues, see attached image for a detailed description and a comparison between how it currently looks and how it should look (simulated using a custom resource pack).
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relates to 2
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Comments 5
i think most of these are intended, not just the head, they all fit in the context of him being inflated for staying in water the whole time.
[Mod] LateLag
One of these issues (The arm one) is already being tracked under MCPE-82082.