Mozart's Piano Sonata in D Major is a stylistically contrasting piece not only in the presence of 12 separate variations, but that within each variation there is evident stylistic contrast that is empirically presented through the harmonic progression, rhythmic variations, and an array of transitions that give each line its own unique feel. Take for example the transition into the portion of VAR. XII that was pulled under the magnifying glass for this excerpt. The transition from measure 25a to 25b introduces a new faster, more excited feel whereas 25a marks the end of a phrase that wasn't as energetic and rambunctious as the phrase from measure 25b to 28a. Not only is the new phrase rather stylistically different and louder than the first, the transition is very abrupt and even the dynamic with which the new phrase is introduced heightens the unexpectedly bright and even highlights the almost uncontrollable excitement with which the new phrase is introduced.
Harmonically the mixture chord may surprise the listener when it appears at the end of the 27th measure in the form of a bVI. Although the Harmonic presentation of this new loud phrase doesn't necessarily posses the most consonant feel, there is definitely a melodic pattern in the bass in the second half of the melody that seems to be drawing the phrase to a close, almost like the phrase was a wild animal now being gradually tamed. The upward motion of the bass in seconds is thrown off a little when the mixture chord is presented as a penultimate to the final chord of the line. The manner in which it creates an interval of simply on half step and turns it into a mysterious almost questioning statement sets the listener up for the chaos that ensues in the melody right after the listener things it will calm down after the cadence in measure 28a.