If a card costs 6 mana, it basically has to say you win the game, and while Dream Eater does a lot of stuff, it honestly doesnt give you any card advantage just tempo, which is a problem for something thats 6 mana
Gameplay in CCG is typically turn-based, with each player starting with a shuffled deck, then drawing and playing cards in turn to achieve a win condition before their opponent, often by scoring points or reducing their opponent's hit points
While there are less instances in modern Pokmon sets where artwork has been censored in this way, these original cards have become highly collectible in the international market
Note that once exiled, they cannot be cast from the graveyards, so this is a break on things like flashback or retrace
Better still, it also gives all instant and sorcery spells in your hand Affinity for creatures, too, making it a highly playable card in Standard, Limited, and Commander.