The trainer hill functions in the same way as the trainer tower in FireRed and LeafGreen. Except that there are only four floors instead of seven. It is only in Pokémon Emerald and it is found North of Mauville City. There are four tag matches:
Each type is harder than the previous one. Your opponents Pokémon level will always be at the same level as the highest level Pokémon in your party. All you get is a Great Ball at the end, which is a bit of a letdown, but it's fun!