Before you say anything, yes, you can breed these. The Catzilla is three times the size of a normal Happy Pets cat, and if you breed two Catzillas, the resulting offspring will be even BIGGER. For a quick size comparison check out the below pic (from left-to-right is a normal cat, Megacat, Ultracat, and Catzilla):

For the record, the Megacat is 1.5 times larger than a normal cat, and the Ultracat is twice the size of a normal cat. But amongst these new feline titans stand the runt of the litter -- Microcat, which is half the size of a normal. Out of this bunch, the Microcat is the cheapest, running players 88 Facebook Credits, or roughly $9 USD. While the mighty Catzilla can be adopted for 198 Facebook Credits, or roughly $20 USD.