By this, I mean the Pokémon that you think have received too much 'hype', when in reality they're just not as good as you thought they would be.
This also includes aspects, or games, and not just the Pokémon themselves.
I'm going to start this off with Mega Charizard X. Only because it became part Dragon type, everyone got excited (or over-excited) with it. Whilst I still think its a decent Pokémon, it didn't need all the attention it had.