Changing your language will not change the language of cards that you have already obtained, only new cards that you pull following the selection
I have a card made with the same basic concept, although i cannot reveal it now, cause it's not finished yet, but still - i can give you a suggestion that might make "Nightmare Phantasm" more attractive to be played with (aside boosting it's original ATK to at least 1200): This card can attack your opponent directly
While Effect Monsters by themselves are a kind of card, Ritual, Fusion, Synchro etc
This fun thing will give your Commanders double strike when they attack
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Best cards : Trafalgar Law (character), Monkey D