I took Pikachu on with my Lv51 Golem. He used Iron Tial on Golem, but Golem had one of those berries that cut a super-effective Steel attack in half. Then when it was Golem's turn he used Earthquake and took Pikachu down in one shot.
I'm not sure if anyone said this yet, but his team is a Level 88 Pikachu, (I think it's 88, definately in the 80's) A Level 84-89 Blastiose, Charizard, and Venasaur. Then an 86-89 Snorlax and Lapras. This isn't in order, the order is randomized, but it starts out with Pikachu, then the three Kanto starters, then Lapras and Snorlax. He has a few Full Restores, and all of his Pokemon are really tough. They gave my LVL 100 Feraligatr a rough time. And they killed my 96 Arceus really easily. My advice, bring some Full Restores and Max Revives. As far as the Pokemon to bring, I'd bring a Rock type, Water type, Fire type, a grass type, and a fighting type. Best of luck!