Discontinuity is an incredible spell that can be used in many useful ways. Obviously, most players will try to use it on their turns for the discounted price.
First, you can play it on your turn to negate the Uro's self-sacrifice ability and keep the 6/6 creature for 3 mana. Second, you can use it on your opponent's upkeep and take an extra turn, which is an excellent option for any control deck.
Lastly, you can use it as a hard counterspell that denies anything your opponents try to do, regardless of if their cards can't be countered. All-in-all, this is a super powerful card that will definitely see play in specialized decks.