Milk Pudding doesn't have an icon, Hypno Cat is using a placeholder (?).
I could be missing more, but these are the two I notice.

@LtxProgrammer , huh, well, you could just just make two textures in the assets folder.
An example from from Fresh Animations Xaero's Icons

What am I supposed to do about this? This mod never had any compatibility set up for xaero's.

Xaero's Minimap Modded Support would also be a good place to look at.

Just checked, the regular shark (that is latex for some reason) also doesn't have a icon.

Just checked, the regular shark (that is latex for some reason) also doesn't have a icon.

i guess it mostly only works for humanoid entities

I've realized how xaero's minimap does it, it uses getHead() of the entity's model. This does not include renderlayers for the model. Hypnocat's stripes are on a separate layer, and the puddle doesn't have a head.

Nvm, reading the code. The render layers are being rendered, but not captured.

This is a little weirder now since eye rendering is separate, doesn't show any eyes for the icons.
I guess making icons would be the best bet.