When you search your discard pile for an energy and attach it to Hippowdon does it have to be the active hippowdon or can it be the benched hippowdon??
d master342 is correct in the answer to the question, but wrong on why. The answer to why it is attached to the active Hippowdon is because whenever a Pokemon says "and attach it to Hippowdon" or "does 10 damage to Pikachu" it should be interpreted as "and attach it to this Pokemon" or "does 10 damage to this Pokemon".
Well, that's basically the same answer. Let's see, if it was to a benched Hippowdown, it would say "Benched". If it doesn't, it means the Active. >__> That's the only simple way to figure it out for yourself.