Derpy Hooves

Flying, Haste
When Derpy Hooves enters the battlefield,
draw a card.
{4}: Draw a card, then put a mail counter on Derpy Hooves. Anypony may activate this ability.
Return to Sender
At the beginning of your end step, if Derpy Hooves
has four or more mail counters on her,
put her on the top of your library.
I just don't know what went wrong. -Derpy