Luckily, most missions only require a handful of cards that you may already be close to finishing, aside from the one that unlocks Mew
Reach vs Hexproof, Protection or Ward What if the attacking creature has flying and hexproof, or another similar ability like protection or ward
It's also a roughly $400 Reserved List card, so probably just stick to Hypergenesis
As sacrificing permanents is incredibly common within the Commander format, as it is done in common archetypes such as aristocrats decks and even when players use the likes of a fetch land, Yasharn can be a huge headache for certain types of decks
Now, with Universes Beyond sets, casual Magic fans buying into the game to chase these gorgeous treatments have driven up prices
And without any dual lands or additional mana fixing, a 16-land deck with an 8/8 split of basics is just barely hitting both minimums