The two creatures may be controlled by the same player.
01-04-2008
wotc
If, by the time Rivals’ Duel resolves, an effect has caused the two target creatures to share a creature type, Rivals’ Duel doesn’t resolve for having no legal targets.
01-04-2008
wotc
If either one of the creatures leaves the battlefield before Rivals’ Duel resolves, no damage is dealt to or by the remaining creature. If both creatures leave the battlefield before Rivals’ Duel resolves, the spell doesn’t resolve for having no legal targets.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.