RE: How much impact will Gengar Prime ACTUALLY have?
Gengar Prime can't reliably put a pokemon in the lost zone each turn. You're right about that, but when the time comes, you might be able to pull off 2, and Palkia G LV.X gets another 2, which compensates for the misses. Spiritomb LL is a searchable "make your opponent draw into a pokemon" card. While Mr.Mime can be a "See if your opponent has pokemon in your hand" card. Maybe I'm wrong, maybe it won't be BDIF, but it'll at least be as good as Luxchomp.
Gengar Prime can't reliably put a pokemon in the lost zone each turn. You're right about that, but when the time comes, you might be able to pull off 2, and Palkia G LV.X gets another 2, which compensates for the misses. Spiritomb LL is a searchable "make your opponent draw into a pokemon" card. While Mr.Mime can be a "See if your opponent has pokemon in your hand" card. Maybe I'm wrong, maybe it won't be BDIF, but it'll at least be as good as Luxchomp.