If you originally created a Speedy Ninja account with Facebook, you cannot combine it with your Speedy Ninja Guest account.
If you have not created a Speedy Ninja account with Facebook, you can transfer the data from Guest account to your Facebook account, with the following steps:
Log in as Guest first -> The Home screen -> Settings -> Log into Facebook.
Please note that once the Guest account data is transferred to the Facebook account, it cannot be undone.
For the character Clucky, it is available for free if you play the game with Facebook. It needs to be unlocked in Guest mode.