The Arena Tycoon of Battle Arena has the following Pokemon-

1. Heracross
2. Umbreon
3. Shedinja

Your first Pokemon should be a Ghost Pokemon,
Second one Fighting Pokemon and this is very important, your third pokemon has to have an attack which is super effective on Shedinja because of its Wonder Guard.

By The Way, If anyone reading this knowns where to catch a Magmar in Pokemon cartridges Leafgreen, Firered, Ruby, Sapphire or Emerald without Action Replay etc. Please mail me at maddyemerald@gmail.com