Happy Pets doubles the fun with new Twin and Coin Idols
Coin Idol doubles the amount of coins you earn from cleaning and petting, while Twin Idol promises that you'll "get twins from every successful breeding." (NOTE: This doesn't mean that you'll get twins each time your pets breed. For that, you'd need the Love Potion or the Love Idol which you can get by clicking on the "Breed" button after clicking your pet.)
The 3-day Coin Idol costs 28 Facebook Credits (or $2.80 USD), while the 7-day costs 52 FB Credits ($5.20 USD). Finally, the 3-day Twin Idol goes for 40 FB Credits ($4 USD), and the 7-day version costs 76 FB Credits ($7.60 USD).