Big Spender Papi

When Big Spender Papi enters the battlefield or attacks, you may buy and open 1 pack of a Modern Legal Booster Set. If you do, then you may choose one card in that pack and exile it face down.
You can look at and cast face down cards in exile. (This is not limited to cards exiled by Big Spender Papi or in your exile. However they must be part of this game.)