Freezer bunny will do too as I've not had it yet. And I have a Sim that is an animal lover and is making friends with the dog so there is hope.
The Mechanical Gnome from Into the Future dies. It has the same tombstone as the Mysterious Mr Gnomes. I just got the three Mysterious gnomes so it will be a while for them to die. I think you need 2 or more to get babies. I hadn't seen a baby gnome until just before I started this thread. Now they appear in my games whenever I have adults. I don't know if the gnome from Into the Future has baby gnomes - but I don't think it does. I had eight of them in my game and they just died.
I am also hoping for the summer gnome to appear too. I was surprised to see the winter gnome turn up. That means I have 3 seasonal gnomes in this game - the most I've had so far. I usually just get Autumn and Spring gnomes.