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This is typically due to consumer demand or people buying them to resell later instead of open

The deck creation cost is relatively low, so if you want to try winning by burn without attacking, please give it a try

A flicker (or blink) deck temporarily removes creatures from your battlefield (usually by exiling), then returns them to play in order to trigger effects that occur when they enter the battlefield

In other words, the bonus sheet cards can't come to Arena with the original Spider-Man comic book art, likely due to licensing reasons, but since they're all reprints to begin with, Arena programmed the entire bonus sheet using art that already existed for these cards