You lose the option on playing it for black and you have to exile the things you return but you will be sacrificing your stuff before then so it doesn't matter a jot
As for Commander, he's been playing since 2010, when he started off by making a two-player oriented G/R Land Destruction deck
When you discover X, you reveal cards one at a time from the top of your library, so any cards that do not meet your discover value of X become the rest and essentially get shuffled before you place them at the bottom of your library
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If neither stat of the new creature is greater, the ability will do nothing
Lurking evil cards are found in Duskmourn: House of Horror Play Boosters and Collector Boosters