5. Lenora (Generation 5)
Oh man, if there was ever to be an award for the most obnoxiously difficult Pokémon, it would hands down go to Lenoras Watchog. The fire-eyed meerkat shamelessly uses hypnosis on your team at any available opportunity, before massacring them in their sleep. Its other moves include crunch and retaliate, which can prove deadly against psychic-types. Luckily, Lenoras first Pokémon Herdier struggles to put up much of a fight, so you should be left with a full party to take on Watchog. Be sure to use fighting type moves to inflict extra damage and pack plenty of Chesto Berries to combat the frequently used hypnosis.