Rosco

"Oh yes! My Rosco does love to play fetch!"

- Riley during the Tea Party

Bio
Rosco was Riley Ruckus's pet dog on Mortimer's Handeemen. The largest puppet on the show, Rosco required two puppeteers to properly operate. Whenever Riley was on screen, her loyal pet was not far behind, often making an appearance in any Riley-centered episodes.

Rosco is a prime example of how insanely scary Riley truly is. Sometime after being brought to life, Riley began experiments on combining puppet parts with organic material, creating many Frankenstein's-monster-esque monstrosities, Rosco being one of them.

Appearance
On the show, Rosco was a very large, blond dog of an unspecified breed, likely some sort of Golden retriever, with a red collar around his neck. Pictures of him in-game have been regarded by many players as "quite cute."

His current form is the exact opposite. Once subjected to Riley's experiments, Rosco's body was deformed into a very large, vaguely canine beast. His jaw is practically detached, with a long, realistic tongue hanging out, his entire mouth lined with jagged teeth. His eyes are completely mismatched in both size and color. The bright red collar has been stained mahogany, and his name-tag is a dull, brassy color. What's left of his fur has gone from a glossy blond to a very dirty blond-brown color, the rest being patches of olive, cornflower and lavender fabric sewed to various parts of his body. One of the paws on his long, thin legs are replaced with a human foot, and the other is two hands wrapped together, with a human arm dangling from his chest. Riley is tucked inside of him, so it's likely that the arm is the unused hand of Riley's host.

The rest of his paws are clawed, which could be from the original puppet, or added when Riley got her hands on him. His teeth are likely made by Riley as well, since the original Rosco has no visible teeth.

Personality
Rosco is shown to be extremely loyal to his owner, Riley Ruckus, as he will obey her every command. While he is antagonistic, it's only when Riley directs him to be, so there's a chance that Rosco hasn't changed from the original puppy puppet.

Riley
Rosco is seen to have a close-bond with Riley, obeying any and every command given to him by her whilst receiving some affection from Riley as well. This could be from the literal sense of being bond to his owner or from the disfigurement Riley had caused the puppet, turning him into her permanent and powerful slave.

Host & Scout
Whilst Scout may not be human literally, since she is alongside the escape-plan with Host as well as being Riley's annoyance, Rosco doesn't appreciate the company from either of them, hence why Rosco will happily obey the command to attack and kill either being on sight if needs be.

Trivia

 * Rosco appears to have been surgically attached to multiple parts of his hosts, making it essentially impossible to separate him from them.
 * Unlike Mortimer and his henchmen, he doesn't acquire a host to live (much like Riley's other experiments like the rats and the miniature dog).
 * It is noted that during the tea sequence, Riley seems physically attached to Rosco, revealing that she has sewn her host into Rosco's body. Seeing as her poster in the beginning of the game notes that "Rosco is her faithful dog who is always by her side", it's foreshadowed that she sewed her host into him so they would never be apart. During the tea party you can see this in action, as when Rosco begins chasing you, Riley can be heard yelling at Rosco to stop so that she can "get inside".
 * Riley frequently shows affection toward Rosco, making the fact she experimented on him all the more gruesome, showing even those she cares for are not safe from her insanity.
 * Judging by his size, color and character in the TV show, Rosco is likely based on the golden retriever.