Cursed Dark Mind

This deck takes a bit of setup, but once it's online, it's incredibly effective at sapping your opponent to death in a most satisfying way.

The general concept is to get a Hypno out as your active, and as many Gengars on your bench as possible, (not requiring energies)

Gust of Wind your opponent's Pokemon with the highest retreat cost (ideally 2+) into the active position, and use Energy Removals to strip them of some energies attached if any. Then play Rocket's Training Gym to further strand them.

This deck takes a bit of setup, but once it's online, it's incredibly effective at sapping your opponent to death in a most satisfying way.

The general concept is to get a Hypno out as your active, and as many Gengars on your bench as possible, (not requiring energies)

Gust of Wind your opponent's Pokemon with the highest retreat cost (ideally 2+) into the active position, and use Energy Removals to strip them of some energies attached if any. Then play Rocket's Training Gym to further strand them. If they play a Switch - your 4x Gust of Winds will pull them back out again. Once they're good and stuck, the fun begins.

Dark Mind (both Hypno and Gengar have this attack) splashes 10 damage to your opponent's bench guaranteed, and does 30 to the active. However, the real magic is in Gengar's Curse Pokemon Power - allowing you to move 10 damage around your opponent's Pokemon, even if it KOs that Pokemon. Which means - if you have multiple Gengars, you can move +10 for every one alive, so you use your opponent's active as a blood bag, and shift damage OFF of it every turn to decimate their bench. If they DO get a Switch off and position something scary as their active - your Hypno can likely survive at least 1 round with it's beefy 90hp, and then when it's your turn, you can use Curse to pull damage ONTO their active + attack with Dark Mind, for a max of up to 70 damage (4 Gengars on the bench, ideal scenario, rarely happens, but still) for the cost of 3 energies which is serious value.

This is not a super consistent deck, but Haunter's Nightmare and Transparency can make it quite difficult to take down despite only having 50hp, so sitting on Gengar evolutions in your hand might not be a bad idea until you're ready with a Hypno to start the process all at once.