Upscaling of creatures and heroes.

There seems to be a mod that upscales everything in Heroes of Might and Magic V.

Yes, there is. Griffin Eternal HD Mod (CREATURESv2.0) – 2k textures at 750MB, and Retexture.pak – 2k with blurry textures from the first one, at 540MB; without the LLA patch, it crashes.

Which one are you playing with?