Making an entity

[ZodiaC]

Excellent! In which case I have another question, I managed to get the billboard into the model viewer and, even though it's upside down, get it into the game. The only problem is the billboard is separate from the water monster and is positioned precisely in the middle of the map D: how do I attach it to the water monster?

As Statyk said you need to create a bone for the water lurker and only then you can attach the billboard...As for the other enemies you don't have to create any bones to attach billboards cause they already have.
Or maybe you could attach the billboard to water lurker with a light!