The colors, the multiple expressions, the angles, the focus of the eyes and different elements zeroing in to a single, tense moment all centrally balanced with surprising amounts of detail with no part overwhelming another.
The wagging dog tail and bell ‘round Pom’s neck actually creates smart use of space while Sparky’s tail arcs in a way to maintain balance and circular focus towards the center and Sparky’s tail arcing. Everything from sweat drops to the angle of Fluttershy’s mouth asymmetrically tilting with Angel’s frown, and the triangle of his nose.
The more you analyze it, the more awesome it becomes, even though it’s bright use of colors and large expressions gives off such an innocent and enjoyably simple piece.
Edited
Angrily, Angel Bunny.