Yes there are such things as TRUE miniature mules. In the registry a miniature mule is anything under 48" at the withers. A TRUE miniature to me is anything under 38". I have 4 now and a possible 3 more coming in Mar/Apr. The biggest is now a 2 yr old out of a 33" mare and a 32" jack. He stands about 37" now. The smallest is last years out of a 30" mare and the 32" jack. At 9 months she MIGHT be 28" tall.
This is Maestro, 4 yrs old, 35". He took Reserve GC mule competing against full size mules.
This is Sunny, 35", true Tobiano mule out of a 30" mare and 32" jack.
This is Jester, the biggest, 37" out of a 33" mare and 32" jack. He is also the sweetest and most loving of the group.
Then this is Miss Wylie. She is just 9 months old, 28" out of the 30" mare and 32" jack. She is a full sister to Sunny.
: She is also the most opinionated, bold mule on the place.
The miniature mules are getting more and more popular. More folks are interested in breeding for them. They just don't realize how much work really goes in to it.