Defeating Karn

Today I finished the standard campaign mode but it took me some time.

The remaining Planeswalkers I had to beat were Sorin and Karn. Sorin played mono black vampires and in the first game showed me some 1/1 bloodthirst bat. On turn two he played Child of Night. On turn three he played Nighthawk which was a problem for Sarkhan's deck I played with. On turn 4 he played Vampire Nocturnus!!! The top card was a swamp but still the next turn he killed me. For the second game I choose Chandra's deck hoping for some burn spells that could take down 5/4 Flyer. I succeeded and could try two new challenges or beating Karn.

I solved the challenges and tried playing against Karn with Nissa's deck (finding out that it is BG). Karn played Mox Sapphire on turn 1 along with Island and Voltaic Key. I was like WTF? But that wasn't the worst. Next turn all I saw was (a weird image) Tinker and Darksteel Colossus on the table. I have to say that I was taken back. I did not expect anything like that. I blocked with my little elf I played earlier and waited a round if I wouldn't draw some removal (not sure if Nissa plays any edicts). I didn't get any.

So I tried it once again. This time I had 2 lands in my hand + sylvan ranger that was there to fetch a swamp for Eyeblight's ending (I had it on my opening hand). Prepared like this I decided to try it once again against the killer combo. Nothing happened though. My opponent played Mox Sapphire, land, Voltaic Key which was soon followed by Icy Manipulator. Later he played two Lodestone Golems and tried to play one elf each turn. Wasn't fun. I had Viridian Shaman and the black removal and waited for something worse than the golems. Steel Hellkite was the first target for Viridian Shaman. Next he played Clockwork Dragon. I tried attacking with Nissa's Chosen hoping he would block with it. I gave my elf +7/+7 killing the dragon and still having Eyeblight's ending for something else.
Few rounds later I decided to attack with everything, use Ezuri's Overrun and play the +X/+X (where X is the number of creatures under your control) spell. This won me the game!