A Journey Through Time

When A Journey Through Time enters the battlefield, choose an era. At the beginning of your upkeep, you may change to a different era.
•Era of Discovery: At the beginning of your upkeep, reveal the top card of your library. If it's a land card,
you may put it onto the battlefield tapped.
•Era of Conflict: Whenever a creature attacks you,
it gets -1/-0 until end of turn.
•Era of Enlightenment: At the beginning of your
end step, draw a card, then discard a card.