If you ask yourself what happens when you win the fight in the memories aggains Siegfried. I did it with an lv. 9 Poliwag and it happens really nothing :Ambivalent: you get 0$ and no exp. After the fight he will "turn you to dust" and you wake up at the Pokemon Center.
But here is a guide on how to beat him:
1. you need an pokemon which knows leech seed. (Ivysaur in my case)
2. one or two pokemon that can put the enemy on sleep.
3. use a pause of his hyperbeams to use leech seed.
4. put him asleep. If he wakes up use your next Pokemon to set him asleep.
and last sorry for my bad english.
have a nice day.