Here's one I've been thinking on since this morning.
You have a {Words of waste} on the field, activate it, then +2 {Jace Beleren}.
Now, both players draw at the same time, yet your draw is replaced by the discard. Will your opponent have the drawn card in hand by the time he has to discard, or does he discard first, then draw?
EDIT: seems I misread the rule on drawing.
120.2a (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=120.2a): If an effect instructs more than one player to draw cards, the active player performs all of his or her draws first, then each other player in turn order does the same.
In other words, unless I draw at instant speed, the opponent discards, then draws.