We currently don't know exactly in what way, given how new the game is, so there's no precise precedent
Countermagic : Mystic Snake, Frilled Mystic, Draining Whelk Reanimation : Karmic Guide, Phyrexian Delver, Extraction Specialist Milling : Manic Scribe, Thieves' Guild Enforcer, Sage's Row Denizen Self-Milling : Stitcher's Supplier, Satyr Wayfinder, Balustrade Spy Discard : Burglar Rat, Mesmeric Fiend, Sin Collector Goading : Insufferable Balladeer, Jeering Homunculus, Vengeful Ancestor "Gain Control" effects : Hostage Taker, Agent of Treachery, Gonti, Lord of Luxury Clones : virtually all of them, though a few are decently pricey
[Counter] Up to 1 of your [Krieg] cards gains +4000 power during this battle
It can quickly become a mana sink as it grows, but Ive seen it used as a counter generator in Ghave, Guru of Spores decks
It's easy to assume only the most expensive and elusive cards on the market would be in contention, but that's not the case
Alternatively, attending local trading card events, and conventions, or visiting dedicated Pokmon card shops can provide opportunities to buy, sell, or trade Rainbow Charizard cards in person