MYTH!  Though Marco's temperament leads him to be chill and happy more often than not, boy have we had our moments!  Fortunately his anger doesn't last for long but because he has no real verbal language it can turn physical.  Ava may have been on the receiving end of more bites than she would like to recall and boy he can cause some serious pain with his chin, LOL!!  So no, Marco is not always happy but he is indeed always lovable!