I did, however, try to keep five of the most powerful and relevant cards at the top of the list, due to their value (in terms of gameplay, affordability, and availability)
Bear in mind though, you didn't really specify a budget, so I'm just going to aim for under $20 per card: Extraplanar Lens (way past 20, oops) Gauntlet of Power (i think this is 20 on the dot) I have to run for now, I'll add voltron-esque cards in another comment later.
Game8's list of Metal Type Pokemon Cards for Pokemon Trading Card Game Pocket (PTCG Pocket)
Its Attack powers are the same as the Super Rare card, with the ability to increase damage by discarding Energy
I find this mechanic very interesting
Spiritomb's design is heavily inspired by the folklore surrounding haunted keystones and cursed spirits, blending these elements into a cohesive and intriguing Pokmon