Hour Of Darkness

Hour Of Darkness etners the battlefield with 12 countdown counters on it.
At the beginning of each upkeep, remove a countdown counter from it.

Whenever you would draw a card, roll a d20, if your result is 16-20, draw an additional card.
If an opponent would draw a card, they roll a d20, if their result is 1-5, they don't draw a card.

When the last countdown counter is removed, transform Hour Of Darkness.