According to the pokedex[1] the Pokemon Zigagoon "always zigs and zags." That statement is logically equivalent to "It never moves in a straight line. If this were the case, Zigzagoon would never be able to move. Consider what a Zig zag really is: a collection of straight lines that weave back and forth. Yet Zigzagoon never moves in a straight line, only in zigs and zags.
This means that in actuality, Zigzagoon is either sessile, or it defies the laws of physics. Seeing as how the Pokedex is inerrant, in fact nearly divine in it's accuracy, we can rule out that it is merely a mistake on the authors part.
Given that other pokedex entries list Zigzagoon as being non-sessile [2], it must be concluded that Zigzagoon breaks known laws of physics. In order for Zigzagoon to move at all, it's movements must be made up of even smaller zig zags, which in turn must be made of even more zigzags. This situation, reminiscent of Zeno's Paradox, results in a fractal like pattern that is extended down to the planck scale where the laws of physics as we know them begin to break down. In fact, it is widely theorized that the erratic movements of Zigzagoon at the subatomic level are the cause of Heisenberg uncertainty principle.
Zigzagoon's subatomic zigzagging are a likely cause of the universe's stability. The universe tends toward entropy at all times. Zigzagoon is a receptacle of this unusable energy. Because Zigzagoon's quantum jitters are closely intertwined with time and space, he can act as an outlet and disperse this energy into extra-dimensional space. The universe's total energy, however, must remain constant. Thus, new usable energy is forced into our plane from other dimensions, ensuring the continued existence of our species. In fact, according to calculations, without Zigzagoon's presence, the entire universe would collapse in on itself within 3 hours.
Footnotes:
[1] - "A POKéMON with abundant curiosity. It shows an interest in everything, so it always zigs and zags." - FR/LG Pokedex
[2] - ZIGZAGOON restlessly wanders everywhere at all times. This POKéMON does so because it is very curious. It becomes interested in anything that it happens to see." - Ruby Pokedex