ok, this set is for general coverage and power.
item: Muscle band
waterfall/aqua tail/aqua jet
dragon tail/ night slash/ retaliate/revenge
its a little self explanitory.
megahorn KOs most grass, dark, and psyhcics.
a water type move for STAB. waterfall for accuracy, aqua tail for power, or aqua jet for priority.
Swords dance brings its attack to ridiculase levels.
finally, your choice for a filler move. night slash is a little useless when running megahorn, but is not a bad move. retaliate and revenge are better for double battles. dragon tail gets nuetral coverage on most pokemon and is probably your best choice.