There are three more UBs other than the ones confirmed.

UB Rotation is exclusive to Ultra Sun. It is Ground/Electric type, and appears as a drill with large jaws. It is said to move through the earth swiftly and silently.

UB Mirage is exclusive to Ultra Moon. It is Ground/Psychic type, and appears as a humanoid feature whose features are hidden by a veil of sand. It is said to strike with blistering speeds, but it is never seen making sudden movements.

UB Sorrow is not exclusive. It is Bug/Fairy type, and appears to be a stag beetle made out of a cello with bows for legs. It is said to inspire melancholy to anyone who hears its cries.