E-061 has its origins vaguely related to Gray City, when investigating Gray City, we found its appearance on an accomplishment trophy in a theatre, which may have been used for trials put against UNAVAILABLE. After Gray City was completely wiped of any alive creatures, Mr. Cat managed to return to Earth.
E-061 is a completely black cat with a white glow attacted to it. It seems to have no facial features, but can easily see, smell and taste, through methods unknown to us at the moment. Its behavior is akin to a regular adult cat, but it gravitates itself towards locations of importance such as Wario's Fast Food Factory and the old Morning Star company building. One major change in its behavior is that it will attack and kill any person who has been injured exactly 9 times prior to their interaction, regardless if these injuries are visible or not, but it will choose to ignore injuries that have been healed completely.