Mandy seems to be the only person capable of taming and commanding it effectively .
Grim owns the giant three - headed dog Cerberus but has no control over it whatsoever and is terrified of it .
Mandy seems to be the only person capable of taming and commanding Grim effectively .
Grim owns the giant three - headed dog Cerberus but has no control over it whatsoever and is terrified of it .