Deck of Many Changes

{3}{T}, Roll a d20. If the result is a 1 discard your hand. 2-6| All creatures on your battlefield gain a -1/-1 counter. 7-11| Draw 2 card, Discard 1 card. 12-15| The next spell you cast has Cascade, Cascade. 16-19| Until the end of this turn, you can cast spells from the top of your library, spells you cast this turn cost {2} less to cast and all creatures you control gain Prowess. 20 | You may cast spells without paying their mana costs until the end of the turn.