Zoroark is a Special Sweeper, with high Special Attack and Speed. His Defenses are awful, but then again... he's a sweeper anyways, so he's not meant to get hit in the first place haha. ^_^
Illusion is neat because, with careful Pokemon placement, it can allow him to get at least one extra turn in, so he can use Nasty Plot. By then he'll have enough power to rip through a lot of Pokemon.
As for Dark Pulse being his best move, it's debatable. Night Burst is slightly more powerful and has a 30% chance to lower the Pokemon's accuracy. But, it has its own accuracy at 95 (Dark Pulse is 100), so there's a bit more risk.
So it's the slightly more powerful and slightly less accurate Night Burst versus the slightly more accurate and slightly less powerful Dark Pulse.
