Piplup is great.Piplup may be weak with a grass type but it's super effective with drill peck and peck.Piplup is super effective with fire types too.As for electric types,you have to envolve piplup to learn dig.Also when you envolve it, you can learn grass knot to beat water types so easily!Don't forget it can also envole to Emploen and learn hydro cannon!And don't for get metal claw either!Piplup is also very strong with it's torrent ability.Piplup is cute and when it envoles to Emploen,it looks tough and it may be too!Also,if you had a piplup, it can learn surf and waterfall when it envoles and then you could meet the champion!Remember,first is a bug trainer so you can beat with flying type moves like peck or drill peck.Next is ground which you can use grass knot.Third is kind of fire so Piplup can beat them easily with a water type move.Last, is a phychic type but I have no advice.Finally,the chamion's strongest pokemon is Milotic so you can use grass knot!