Instant, 2UU (4) Untap all creatures you control and all creatures target opponent controls. You and that opponent each gain control of all creatures the other controls until end of turn. Those creatures gain haste until end of turn.1
Illus. Colin MacNeil
It is perfectly legal for either or both players to have zero creatures. They give control of all their zero creatures as instructed. [Barclay 1998/02/27]
If any of the creatures phase out, the control effect ends for those creatures, and the creatures will phase back during your next untap but under their original controller's control. [D'Angelo 1998/06/01]