The main difference between a proxy and a real card is the rosette pattern
You always want to have access to all your colors so you can cast any spell that may find itself in your hand
The biggest danger is that almost every deck sideboards Karn, rather than that Karn just beats everyone, and I think theres a good chance that wouldnt force them to ban Karn, although theres a small chance that that would push the price of Karn high enough to chase some people out of the format.
If you do, return Akuta, Born of Ash from your graveyard to the battlefield
This deck is aggressive, has a lot of play to it, and offers excellent sideboard options and varied threats, which makes it difficult to fight against
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