The first is that Pokmon doesnt want diversity anymore

Other CGC Trading Cards-certified Pokmon cards in the auction included: a Pokmon (1999) Base Set - First Edition Complete Trading Card Set graded CGC 7 to CGC 9.5 (lot 36156) that realized $40,800 a Pokmon (2000) Neo Genesis - First Edition Complete Trading Card Set graded by CGC (lot 36162) that realized $10,800 a Pokmon (2000) Gym Challenge - First Edition Complete Trading Card Set graded by CGC (lot 36161) that realized $5,160 a Pokmon (2000) Team Rocket - First Edition Complete Trading Card Set graded by CGC (lot 36159) that realized $4,800 a Pokmon (2000) Gym Heroes - First Edition Complete Trading Card Set graded by CGC (lot 36160) that realized $3,960 Other CGC Trading Cards-certified Magic: The Gathering cards in the auction included: a Magic: The Gathering 1992 Gamma Playtest Edition Lightning Bolt graded CGC 7 (lot 36060) that realized $6,300 a Magic: The Gathering 1993 Unlimited Edition Timetwister graded CGC 6.5 (lot 37085) that realized $5,040 a Magic: The Gathering 1992 Gamma Playtest Edition Fireball graded CGC 7 (lot 36050) that realized $4,560 a Magic: The Gathering 1992 Gamma Playtest Edition Fear graded CGC 6 (lot 36048) that realized $4,440 a Magic: The Gathering 1992 Gamma Playtest Edition Jump graded CGC 7 (lot 36059) that realized $3,840 Pokmon and Magic: The Gathering cards represent a rapidly growing segment of the collectibles market

But while Melmetal is likely to be your heavy hitter, for this deck to be at all viable, you're going to need two copies of Dialga Ex
This is because when this seven-mana 7/7 enters the battlefield, its controller can search their library for up to five Dragons with different names, revealing those cards, and putting them in its owner's hand