Five mana is a bit steep but in the late game it matters a lot less about the cost and a lot more about the immediate impact, this flexibility makes the card much stronger rather like Mull Drifter which is somewhat of a back up plan in one of its curve slots
If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so
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FromTheShire: Dreadbore already sees somewhat fringe Modern play, and with plenty of ways to trigger descending like fetches etc this could certainly see a bit of play as well
Then, for each nonland card thats milled that way, they lose one life and remove a rad counter
And while they dont offer the defined strengths of reds burn or greens big creatures, MTG colorless cards compensate with incredible versatility, making them indispensable for anyone looking for the highest-tier MTG cards to round out their deck