I also need advice for fighting Cynthia in Platinum because I just go to the Elite Four.

Weavile. All imma say.

I don’t have a Sneasle-
Plus I’ve already lost to her once.
I might as Well put in the Effort to grind a Sneasle and then evolve into a Weavile.
I have a razor Claw,

Weavile is faster than garchomp and hits like a truck with STAB 4x moves. Every platinum play through I have ever done I have always used Weavile for that very reason

When you’re too lazy to wait until night to evolve your Sneasle so you hack your DS time to evolve your Sneasle