Being a Poison-Type, I am immune to ALL Deadly Neurotoxins! Or really, anything that's poisonous in general. You, forgetting this, do not realize that I've merely set up a decoy to fool you to try to take the hill I never left. I ambush you and use Toxic on you before you get close to the top-and it lands. You're too sick from all the subsequent puking to face me one on one, so you go to the nearest Pokemon Center, which is in Nowhere-near-the-hill-ville (which is rather non-indicative, but not TOO non-indicative), and I reclaim my Hill.

MY HILL!!!