The Keeper of Favorite Cards (UNK-RW90A) - Unknown Event

Whenever The Keeper of Favorite Cards enters or attacks, choose a nonland card name and add it to your favorites list for this game. (You can have limitless favorites.)
Your favorite creatures get +1/+0.
Whenever you cast one of your favorite noncreature spells, create a 1/1 white Soldier creature token.