Pokemon: 16
Strategy:
By using Dark Corridor, the opponent's active is poisoned and Gengar switches out to the bench. If Virbank City Gym is in play, then the poison will do 30 damage in between turns, which is why you choose Trevenant when switching out. If Dragalge is in your bench and Trevenant is in the active, then your opponent can't retreat or play item cards, so if there is a card you want to defeat in your opponent's bench, you can Pokemon Catcher or Lysandre, then use Dark Corridor and switch with Trevenant. If Dragalge is in your bench, then your opponent can't retreat leaving them with very little options. I also run Zekrom to counter Yveltal and Reshiram to Counter VirGen. Sigilyph could also help stall if the active Pokemon is an EX. I added in Float Stone for free retreat when I need to get back to Gengar, but if there is an item lock from Trevenant and Seismitoad, then I can attach a Mystery Energy for two less retread cost.
I would like to add in more things, but it is difficult to squeeze them in.
3 Gengar EX
3-3 Trevenant
2 Sigilyph LT
1 Reshiram BW
2-2 Dragalge
2 Bicycle
3 Ultra Ball
2 VS Seeker
1 Escape Rope
3 Robo Substitute
1 Professor's Letter
2 Evosoda
4 N
4 Professor Juniper
2 Colress
2 Lysandre
1 Skyla
3 Virbank City Gym
1 Computer Search (Planning to replace for Dowsing Machine)
3 Float Stone
6 Psychic Energy
4 Double Colorless Energy
Strategy:
By using Dark Corridor, the opponent's active is poisoned and Gengar switches out to the bench. If Virbank City Gym is in play, then the poison will do 30 damage in between turns, which is why you choose Trevenant when switching out. If Dragalge is in your bench and Trevenant is in the active, then your opponent can't retreat or play item cards, so if there is a card you want to defeat in your opponent's bench, you can Pokemon Catcher or Lysandre, then use Dark Corridor and switch with Trevenant. If Dragalge is in your bench, then your opponent can't retreat leaving them with very little options. I also run Zekrom to counter Yveltal and Reshiram to Counter VirGen. Sigilyph could also help stall if the active Pokemon is an EX. I added in Float Stone for free retreat when I need to get back to Gengar, but if there is an item lock from Trevenant and Seismitoad, then I can attach a Mystery Energy for two less retread cost.
I would like to add in more things, but it is difficult to squeeze them in.