Creating three tokens for 3 mana is going to be good and will trigger a lot of the other cards in your deck nicely
This isnt feasible in real life scenarios, such as situations where you have someone breathing across from you
Black tends to work best for milling when paired with blue, because its small attacks do advance a milling strategy
IIRC in Yugioh there is only a certain number of Blue-Eyes (from the show?), so you could put a rule on the card 'there may only be X Blue-Eyes on the battlefield at any time', Star Wars CCG used to have permanents that you could have 2 or 3 copies of in play, in addition to stuff you could only have 1 of, the concept would work fine here too, only this could care about both players' boards
In many cases, it appears as a point/counterpoint exercise aimed at eventually explaining why a card will or will not work
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