Thus far Mr. Mucky has not had the effect we were hoping for. In fact, we've had something of a regression where our son is having to be reminded to go to the bathroom on a schedule or else he's having an accident.
It's frustrating, to say the least. Things started very promisingly. He was very interested in the little story I made and talked a lot about Mr. Mucky wanting to go on the waterslide (the toilet) instead of being squished.
Hopefully this is only a temporary setback. I keep hearing how it is not unusual for children with autism to regress as they're learning a new skill.
We'll keep trying this tack awhile longer.