Depends on your room steward. Most will do a different animal every night (except on the first day when they are over worked trying to clean the cabins for the new cruisers and then again in the evening.
I have never gone a whole cruise without seeing towel critters. But I have had stewards that were only good at one or two types. Most will use your sun glasses or something else to decorate the things too.
Really depends on the demeanor of the cabin steward. I have been on cruises when I get them every day and I been on some where I might get maybe two in seven days. Who knows... just place a quarter under your pillow and pray that the animal towel fairy visits your stateroom.
Our room steward was awesome...he did an animal every night and everynight we saved them so that at the end of the cruise we could take a "family" picture. Well on the third night he made the first animal disappear. We kindly asked him if there was a way that he could let us save them until the end of the cruise for the picture. he did!! he re-did the first animal and saved the others. At the end of the five night cruise we had a whole zoo on the window sill (we were in a porthole room) and it was awesome!! loved our room steward!!
A sure-fire way to get a towel animal every night is to tip your room steward on the first day or second morning of the cruise. We tipped ours several times because she was very responsive to our requests and just a nic gal all around. She worked hard and deserved it.
And yes, we got a towel animal every night, starting the second night of the cruise.
We have always been lucky enough to open our cabin door and find a sculptured animal towel waiting for us. Perhaps, it's because we've had our children with us. It's always good for a laugh. Especially when the cabin steward uses your sunglasses/eyeglasses or baseball cap as "props".
The animals have always been on the bed, with the next day's Carnival Caper, 4 squares of Carnival Chocolates and, (if you have children) chocolate chip cookies.