@khahan
The choice between Snapcaster and Mission Briefing is highly dependant on your build and what role you want/expect it to perform. I do run two Gifts Ungiven/ Thirst for knowledge in my deck since I'm heavily relying on the Salvagers/Pyrite Spellbomb combo, so, Mission Briefing might give me more mileage than Snapcaster. Although, Snapcaster doesn't get hit by Flusterstorm, so, there is that.
My only gripe is the double blue for Mission Briefing.

This card is definitely not easy to evaluate without further testing.

I'm testing one in bomberman and a playset in Legacy solidarity minus the Snapcasters. So far, feels better than SC in solidarity since it actually digs us further into our deck and more likely to chain multiple Mission Briefing ,thanks to Hightide.

@moorebrother1 this would be in the realm of a Dark Depths deck.
Also, I stopped running discard in any deck I played that didn't have a quick combo finish, like AdNauseam tendrils, or heavy disruption like Humans.dec to make up for/maintain tempo.
Take Thought-knot seer as an example. I can turn one TKS and I'm way better off than if I turn one Thoughtseize. Simply because of the threat it provides. Even if the opponent deals with my TKS, the opponent is playing into my game now.

my two cents.

@grr Holy light seems good in a Empty the warrens or Pyromancer heavy meta. Any one-sided board wipe is worth considering in Eldrazi decks of all variations.

Time to dust off my city of brass and put them back in a blue deck with Big-Niv in it.

I like Varina, the Lich Queen better at least in a Pitch Dredge variant.
Still seems a bit "win-more"?
Needs testing for sure.

Thank you for posting this.

For a second there, I thought Grayscale Eldrazi would be something completely different. .

I really like this card. Will most likely try two in a deck and go from there.
Edit: only reason I dislike this card is it's worse than thoughtsieze against shops.

@vaughnbros
Any vids to see you/this list in action?
I saw LSV run his Dredge list a day ago, I think, but he runs 4 Bridge. I Don't really enjoy his streams much though.

@blindtherapy ok, maybe slightly. Lol.
but I think NTDH is where it ends.
At its worse, Yuriko is a Ninja of The Deep Hours. At its best, it's a serious clock that will close the game in a turn or two, without really jumping through hoops. (In Standstill, at least)