It is a very odd mana rock, because you are spending mana to get 1 less than you spent, but I think the threat here is that it then also becomes an 8/8 that makes opponents start sacrificing permanents, which seems pretty strong, especially since it is safe from creature-based removal until you turn it on
Then, it enters the battlefield with +1/+1 counters equal to the highest mana value among all cards in exile, both yours and your opponents
He dropped Karn and targeted me with the +4 ability, and the card I exiled was Brooding Saurian
Rohgahh of Kher Keep is a Legendary Kobold, and we'll talk a bit more about Kobolds in Red
Y'shtola Rhul Doubling the end step
Shuffling: Consistent shuffling and deck handling