Just change slash for one of it's STAB moves and you're ready to go. If you manage to spore something, he'll be forced to switch, so predict that switch and paralyze the incoming pokémon with stun spore. If you paralyze a pokémon you won't be slower... you can sweep with marowak if you paralyze some of your opponent's pokémon.
What's it's full moveset? Mine has Spore, seed bomb, x-scissor (both STABS) and aromatherapy. It can learn stun spore by level, not a bad move. Swords dance could be ok if you plan to sweep, but it's really slow... Brick break for coverage (to hit all things that resists it's STAB moves). Can get sinthesys by move tutor, as well as knock off.
It's movepool is not huge, but it has some decent options.
I really like parasect ^^
you should give your parasect x-scissor and seed bomb over slash. They're stab (same type attack bonus), so they get +50% power, that means 120 power!
x-scissor is a TM I think. Ask Itsang to clone it. You can get seed bomb in the battle tower tutor.
hey, am your oppnent on the PC tournment for the 4th gen :) so i just wana let you know that ill be available on thursday or friday, ill VM you when am ready to battle