who did you find the toughest of the 5.

Will - psychic
Koga - poison
Bruno - fighting
Karen - dark
Lance - dragon

So far for me, its lance.

Strategy for Will - use ghost moves
strategy for koga - use psychic
strategy for bruno - use psychic, flying, and one water move
strategy for karen - use fighting moves or bug. When she uses vileplume, use fire, when she uses gengar use psychic.

The first pokemon lance uses is gyrados and that I have yet to get passed. He uses waterfall, ice fang, and dragon pulse that I know of.