Wouldn't a BG decklist be the best? Running things like Veteran Explorer (or other "both players search for X lands"), Ghost Quarter's, and Assassin's Trophy? I think it would be pretty easy to get a "lock" on opponents Mana with this, land search/strip effects, and Null Rod/Ouphe.
The rules allowing you to look at a player's sideboard while controlling their turn where changed in 2016 because of Emrakul, the Promised End. You are no longer able to do so and you cannot choose cards from outside the game with things like wishes or Karn's -2.
Source: Gatherer entry on Mindslaver
this card has some keywords which elevates it far above what you compare it to (ashiok/censor)
Censor is the most comparable, but the effect is far better (basically don't search if "may", game over if mandatory search).
Ashiok has the same effect and has to be removed. So does this card to a similar extent, because it it a 3/2, which is sometimes better and sometimes worse than ashiok.
But flash makes this sooo good. It's the first time we had this effect on instant speed, and at a affordable cost. Now any fetch will threaten ritual/this. Backed by Daze this will be so obnoxious to deal with for decks reliant on fetches and tutors.
Probably more in Legacy without fast mana.
PS: This is a control player effect at instant speed for 3 mana, if conditional, on a 3/2 body. I am pretty sure that this will see play.
I would just like to note that if this translation is accurate, you control the player, like mindslaver, so you get to see their hand/sideboard/morphs when resolving their search.