Another beta patch was released and a new achievement reward was discovered! [source]
New Achievement Reward
Completing the achievement Pro Pet Mob (raise 75 pets to level 25) will reward players with a Singing Cricket.
Whether or not this pet will actually sing, like its name implies, is unknown. If it does, perhaps it will take song requests!
New Possible Guild Pet
The guild vendor was updated with some new items, including a new possible pet, the Thundering Cloud Serpent Hatchling. There is also a mount of similar name currently priced at 3,000 gold.
For the time being, the Thundering Cloud Serpent Hatchling does not have a sale price, and the item on the vendor appears to only be a placeholder. Much like the Dark Phoenix Hatchling, it's likely that this pet will be a reward for completing a guild achievement. We'll just have to wait and see which achievement will be necessary to unlock this mystical companion!
MoP Beta: New Achievement Reward and Guild Pet
May 10, 2012