Gholdengo's ability lets you draw one if on the bench, two in active, which is great card advantage. But that's not all! Its only attack costs 1 metal energy and can do up to 550 damage (by discarding the remaining 11 metal energy in the deck).
The support cast is made up of:
Lady - which lets you search for four energy
Superior Energy Retrieval - which lets you set up again after an attack
Adaman - which can discard your extra metal energy to tutor two cards (i.e. Super Energy Retrieval to get energy back and something else pending situation)
Lumineon - to find your Lady and Adaman
Arceus Vstar - as a backup attacker and tutor
Squawkabilly and Bibarel - to refresh your hand
And a general unoptimized stew of pokeballs, supporters, and other items.