I could complicate it more.
If the Charmander has a Lum/Chesto berry than Prasect can out speed with a Choice Scarf (174*1.5 = 261 which is larger than Charmander's 251, both with +speed nature and max evs/ivs) and can one hit with Return.
If Charmander has a scarf as well than it beats Parasect with a scarf.
If Charmander has a scarf it won't be able to one hit Parasect with an Occa berry or Focus Sash and can counter with Spore/ Return.
If Parasect has an Occa or Sash than Charmander will always out speed and can use a Lum or Chesto Berry to counter Spore but dies to Return.
If Charmander has a Sash and uses a fire attack than Parasect wins if it uses Spore or loses with Return.
If Charmander has a Sash and uses Taunt than Parasect wins if it uses Return and loses with Spore.
Edit: Yay for contradictions.
[Edited by ghost42, 8/22/2011 2:03:53 AM]