In that vein, this is basically Vicious Rumors + Divination. I would almost certainly say this effect is UB, with a generic mana component to bump it up to a fair total mana cost.

More interesting is that "exile 5 cards at random from your graveyard" portion. This is almost certainly not worth retaining as is. What if I have half my Yorion deck in my yard? Can you imagine trying to randomly generate 1-40, then 1-39, etc in a live event? No thank you. Imo, this should just be "exile 5 cards from their graveyard."

Divination plus Vicious Rumors would be UB2. I'd say this is slightly more powerful than just that though. UB3 is almost certainly fair.

I think it's more interesting to ask why you need this effect explicitly?