original 150 pokemon cards value TCG: 151/150 Complete Base Set 1999 MP-NM Condition (45 HOLOS) Original 151 Complete Set (151/150)

One fan discovered that he's been sitting on one of the rarest MTG card collections in the world and it's worth around $1m

That's realistically a better version of the above card, and is standard-legal.

Choosing past mills cards, and then each opponent takes damage equal to the mana value of the milled cards

(Translation) 1 2 Pocket Monsters Encyclopedia

Looking for Mega Froslass ex prices and values

Some upgrades at your price point to consider: Esper Sentinel, Mystic Remora Diabolic Intent, Fabricate Skullclamp (in the precon), Baleful Strix (in the precon) Ornithopter of Paradise, Signets and Liquimetal (in the precon) The Reality Chip + Sensei's Divining Top combo Spellskite, Skrelv, Defector Mite, Ethersworn Canonist Skrelv's Hive Counterspell, Swords to Plowshares (in the precon) Good luck with your deck