Mutual agreement

During your upkeep before drawing and untapping, look at the top card of your library, then name 4 card types, one of which must be the same as the card you viewed, then play that card face down. Your opponent must guess of the 4 types what the card type is, if they are correct, discard it, if they are wrong, you may cast that card without paying it's mana card then repeat this process. Each time you do add a counter, when you have 4 counters, transform this card.