As far as I can see Drapion is a problem for Ash...
But then again, Ash has had difficulties with any Drapion he encountered.
Going by how the battles has progressed up to this point i'm impressed by how both trainers learned from each others tactics and devise new tactics (e.g. the flare blitz underground to remove the poison spikes).
I expect the final battle to be between that annoying yellow mouse and Electivire after Gliscor weakened Electivire.
Both knock each other out, but Ash his pokemon wakes up a little sooner after being called out.
All of this based on the fact that Ash will have to face the Darkrai trainer.