Each time a spell or ability instructs you to flip a coin, you may apply Pokey’s second ability as a replacement effect to roll a d20 instead. If the result of that roll is 1-10, the original spell or ability sees the result of the flip as tails. If the result of the roll is 11-20, the original spell or ability sees the result of the flip as heads. If the result of the roll is somehow less than 1 or greater than 20, the original spell or ability doesn’t see heads nor tails (you’ll have to read the effect carefully then to determine what happens).