Nice, turns your creature into a Somnophore!

Well, kind of a Somnophore. At last you can target different creatures every time.

This thing is surprisingly great for a common card and lot of people are digging this new ‘Cipher’ mechanic. For those of you that are not 100% clear:

From the WOTC official Gatecrash Mechanics page:

“

As a spell you control with cipher resolves, you may exile it and choose a creature you control. The cipher card is then encoded on that creature, and whenever that creature deals combat damage to a player, its controller may copy the encoded card and cast the copy without paying its mana cost. Usually, the creature’s controller will be you, but if another player takes control of your creature (due to something like Act of Treason, for example), it takes the encoded spell with it to its new master.

Some of the finer points:

• After you copy the encoded spell, it remains encoded on the creature (whether you cast the copy or not).
• If more than one spell is encoded on a single creature, you can copy any or all of them when that creature deals combat damage to a player. You can cast the copies in any order.
• The copies created by the triggered ability can’t be encoded on a creature.
• If you cast a spell with cipher, encode it onto a creature, attack with that creature, and deal damage with that creature, you’ll get to cast that spell twice in one turn.
• The spell’s instructions are followed in order, so exiling it and encoding it on a creature is the last thing you’ll do while resolving it.

In the case of Call of the Nightwing, that last bullet point means you can encode the spell onto the creature token the spell itself just created.

”

You’re basically actively tapping down creatures versus passively with cards like Gideon’s Lawkeeper (which were just a pain in Limited). This like any of the other Cipher spells are great with cards like  Invisible Stalker, but that has been talked about many many times.