Creatures with shadow can only be blocked by other creatures with shadow. This means that Shadow Rift is more than likely going to give you at least one unblockable creature for one turn, or allow you to block one of your opponents creatures that he thought was going to be unblockable this turn. The only thing you have to do is choose your creature wisely. I like to use it on Fallen Angels or other pumpable creatures. Or any creature that will kill the attacking creature, if I have to use it on a blocker. Abu Ja'far is truly unfriendly given shadow and used to block a creature that was supposed to get through your defenses. Then you get to draw a card.

Shadow Rift's dual nature makes it useful even if you are not attacking or blocking. I have used Shadow Rift to simply draw the next card, particularly if the game has degenerated into a standoff and I am desperate for a game breaker, or even the second part of a lock combo. I am particularly fond of any card that allows me to get to my combos more quickly.

Lest you think that I only like to use Shadow Rift to get to my other combos, let me assure you that I usually have particular uses in mind when I include a Shadow Rift in a deck. I like to use it on Fallen Angels as I have mentioned as well as on any very large creature, like Force of Nature or Polar Kraken. Just think of all those cards that have special abilities if they get through unblocked, like the Murk Dwellers from The Dark expansion, Necrite from Fallen Empires or Ophidian from Weatherlight. Really any time you want to be reasonably sure that a creature gets through your opponent's defenses a Shadow Rift is a good bet, and since it's an instant you get that element of surprise going for you also.

I like clever cards and Shadow Rift is a very clever card. It had two distinct uses and the element of surprise. No wonder I like it!