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So if I play Genesis Hydra (let's say for the sake of example, X equals 5). I reveal the top five of my library and I choose Nessian Game Warden and he goes on the field. At this point, does Game Warden's etb effect go on the stack prior to me shuffling the cards into the library ? If yes do I treat the cards I revealed as though they were still in that order on the top of my deck? If no, I shuffle them back in and then look at the top X or set the revealed cards aside and look at the top X prior to shuffling them in?

This isn't a super important question and it's unlikely it will be game changing but I want to know exactly how it works for future reference.

Thanks in advance!