1st - Used Turtwig in Diamond, and Piplup in Pearl. Easy
2nd - Starvaria (D) and Ponyta (P). Double easy
3rd - Starvaria (D) and Prinlup (P) took down Lucario easily.
4th - Grotle, Pachirisu (D) and Luxio (P).
5th - Grotle's Bite (D), and Luxio's Bite (P)
6th - Torterra, Floatzel Lucario (D), Empoleon and Carnivine (P)
7th - Torterra and Lucario (D), Rapidash (P)
8th - Torterra (D), A little of everybody (P)
Nothing hard about it. Just have the right moves