Princess Celestia

Eminence When Princess Celestia is in the
command zone, all Alicorn and Pegasus creatures
cost {1} less to cast.
When Princess Celestia is on the battlefield, all
non-flying creatures get +1/+1 and have vigilance.
If all four Alicorns are on the battlefield at the
same time, they each get +2/+1 and have double
strike