Catastrophe
As long as Gengar is your Active Pokémon, if one of your opponent's Pokémon is knocked out, that Pokémon is placed in the Lost Zone.
Cast into Darkness
Look at your opponent's hand. Select a number of Pokémon in their hand equal to the amount of Energy attached to Gengar and move them to the Lost Zone.
Cursed Drop
Place 4 damage counters on your opponent's Pokémon in any way you like.