The Pufferfish mob was added in 1.13 during the aquatic update. It starts in its tiny phase and gets bigger as the player gets near. If attacked it goes straight to large puff. https://minecraft.fandom.com/wiki/Pufferfish
There is a fold line and no fold line version of each Pufferfish. The fold lines, letters, and cut indications should give a good idea of how to make the design.
The medium puff does not use the same exact texture as in minecraft because the original has some texture errors due to using the spikes from the large puff. This is what I think it would look like if they fixed that.
Click on the papercraft design image.
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