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The Magic Chest 30: Unnatural Selection
Changing a creature's type has never been as easy as it is with Unnatural Selection. Sure, there's Conspiracy, but that only affects your own creatures and it can't be used to pull dirty tricks like turning your opponent's merfolk into bunnies so they don't get the Lord of Atlantis bonus anymore or turning someone's goblins into elves every turn to stop those Goblin Grenades. And that's just the beginning.
My first attempt at an Unnatural Selection deck focused on elves. It used Eladamri, Lord of Leaves to make them untargetable, Elvish Champion to pump them and Unnatural Selection to turn Eladamri and the Champion into elves, so they got their own bonus. The deck didn't turn out to be very interesting, though, and I quickly realized I was much better off using Overrun instead of Unnatural Selection.
So, back to the drawing board. A good replacement for elves turned out to be slivers. Crystalline Slivers replace the Eladamris and Muscle Slivers the Champions. A few Winged Slivers provide evasion, a Talon Sliver helps on defense and Victual Slivers work as bears and provide the potential for lifegain against burn.
A total of 15 slivers is enough as a skeleton crew for the deck. In tournament level sliver decks, Survival of the Fittest used to be a pretty popular card, because it can get the right slivers at the right time. There's nothing like fetching four Muscle Slivers in a row and making them untargetable and flying. It also allows me to play single copies of some useful creatures. Two is enough, though, or the deck becomes too focused on winning and not enough on nasty Selection tricks.
Unstable Shapeshifter is a surprisingly powerful addition to the deck. With an Unnatural Selection in play, you can get rid of any creature your opponent plays by turning your Unstable Shapeshifter into a legend, followed by the creature. Because the Shapeshifter has the same name as the creature, there are now two legends with the same name in play, which means the one that turned into a legend last dies. Sure, the Shapeshifter is vulnerable to removal, but if you have a Crystalline Sliver in play, you can turn it into a sliver to protect it.
Another nasty thing to do is to turn all lands into creatures with Nature's Revolt and to pick off any double ones by turning them into legends. This is especially effective against monocolored decks, but it's a bit tricky to cast, considering it costs five mana, so most of your lands will be tapped, giving your opponent a big creature advantage on his next turn. For that reason, it might be tempting to use Jolrael, Empress of Beasts instead.
Another use for Unnatural Selection is to turn walls into creatures which can attack. The two walls that are good candidates for the deck are Sunweb, because a 5/6 flying creature for 4 mana is pretty good and Jungle Barrier, because it's a cantrip and has enough power to make attacking with it useful, especially when it's turned into a 3/7 sliver. I finally decided on the Jungle Barrier, because the cantrip makes it useful to keep my hand filled.
Coastal Drake is a good creature at 2U for a 2/1 flyer. But with a Selection in play, its ability to return a kavu to its owner's hand can really frustrate an opponent. Alternatively, it can be used to bounce a Jungle Barrier for extra card drawing.
If you're lucky or rich enough to own a King Suleiman (1/1 for 1W. Tap: destroy target Djinn or Efreet), I'd change one Coastal Drake to it, just because it works so well with Unnatural Selection.
Another card that works well with the Selection is Knight of the Mists. When it comes into play, pay U or bury target knight. A blue Nekrataal.
A bit of drawing power in the form of Fact or Fiction will help you recover from mass removal like Wrath of God.
I'd like to have at least eight counterspells in this deck, but I could only find room for four, so I've put Force of Will in the main deck and Foil in the sideboard, to be sided in against decks that are low on the creature count.
Getting the land right is a bit tricky, especially if you don't have dual lands. If you want to put early pressure on your opponent with slivers, you need to have access to all three colors as early as possible, so I made sure I had at least 10 sources of each of my three colors of mana.
With only 20 lands, it's a good idea to sideboard against land destruction. Sacred Ground is always a good choice. A few Disenchants to round out the sideboard and the deck is finished.