I just spent a half-hour slaughtering 11/12 T50 decks with this odd-looking but extremely fun Life/Darkness deck:
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The deck plays like a typical Life speed deck most of the time, with lots of fast Cockatrices dropping and getting pumped up on Epinephrine, and Feral Bonds triggering off of Cockatrices and Emerald Dragons.
The difference is of course in the darkness cards. With only a Mark of Darkness, you have to be very careful when you play them, but the ability to Steal permanents is a great defense-breaker, and more importantly the two Liquid Shadows have amazing versatility. They can be slapped on a Jade Dragon to give you 8 turns of +11 life/turn additional healing beyond the Feral Bond and Jade Staff, which is just phenomenal -- or, they can be used on an enemy 'skill' unit to essentially Lobotomize and eventually kill it -- perfect for that annoying Arctic Squid or Firefly Queen.
Out of a dozen T50 games, I won 11, Mastered 5. This deck crushes Rainbows in a bad way - with the revised Sundials only stopping attacks for one turn, and Adrenaline taking down Bone Walls easily, and Steal for the other defenses, it's like taking candy from a blind, crippled baby. Other speed decks have trouble keeping up with the lifegain that happens at the same time as the speed beatdown comes. The one loss I took was to an all-life Flying Morning Glory deck that featured Shard of Divinity+Miracle, and even that I brought down to 3 HP and no cards in hand before the 8-damage spam caught up with me.
[edit]Oh, and I tried it with Giant Frogs, etc., but it's just sweet to have a speed beatdown deck with absolutely no Otyugh fodder in it.
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