You should get into the habit of backing up more often. Did this happen when changing lands. ?
Here's something to try, but I don't know if it will work.
First, go to My Documents\Black & White 2, find your profile and copy it to your desktop. Now rename it to something else but keep the tildi (~) at the beginning of it. Now move this folder back into the profiles folder. It will show as a new profile when you start the game. Now go into the Autosave folder of the new profile, sort it by time and delete any folders created since this problem started. Now look for the profile.ini file in the profile folder and open it with notepad. (right click, "Open With") and look for the creature name, now change this to the name of this profile. It should look something like L"P_r_o_f_i_l_e". Save and start the game. Now go to the new profile and see if it will load and if your creature is normal again. If not then delete some more of the saves until he is. If you can recover him this way, then you should be able to go to your normal profile, delete those folders and get your creature back.
I have not tried this, that's why I'm recommending to use a test profile first.
Good luck.