The Time Experiment

Suspend
Look at the top three cards of each player's
library. Pick an instant or sorcery spell from
among those cards and exile it face down. When
you cast this spell, you may reveal an exiled card
that was exiled this way and add its text to this
spell as it resolves. If you do, put the revealed
card on the bottom of its owner's library.
Exile this card and put three time counters on it.