I like how everyone is posting decks with Lost World and Gengar Prime. So, here's the counter. It can defeat even VileGar, not to mention new hand every turn.
Pokemons:
4x Skarmory UD
3x Dialga CL
1x Dialga Lv X
3x Magnemite Lightning SF
2x Magneton TU
2x Magnezone Prime or 1x Magnezone...