Magic: The Gathering - Duels of the Planeswalkers

Go to "Challenges", and select the very last one, Sarkhan Vol. Wait forever until it loads.Your first action will be to play the FREE Summoner's Pact, pulling Eternal Witness from the graveyard. After she's in your hand, you're going to cast Harrow, sacrificing a tapped mountain or plains, and pulling out a forest and a plains. Repeat with the second Harrow, pulling the other forest and plains from the deck. Now, you'll need to activate Khalani Heart Expedition, which will have four counters, and allow you to pull two more lands. Then, use the Elvish Piper's ability, paying one green mana to put Eternal Witness onto the battlefield. With her ability, you'll take back one of those recently cast Harrow spells. Finally, recast the Harrow, sacrificing whatever land you want, and pull your last two lands from the deck, thereby taking eight lands in total, and a completed achievement.

Please see my video below, as proof.

The strategy I used was a little different but still works. As RitzOmega stated you'll want to do the last challenge of Expansion 2 (obviously).

Same strategy applies at the beginning, use Summoner's Pact to pull Eternal Witness from your available green creatures. Next step is to cast Harrow and sacrifice a Mountain. Bring out a Plains and a Forest. Cast your other Harrow and bring out another Plains and Forest sacrificing another tapped Mountain. Sacrifice Khalni Heart Expedition. Bring out the 2 Mountains. Use Elvish Pipers ability to bring out the Eternal Witness. Now this is where I did it different. I brought out a discarded Mountain from my Graveyard then played it. Then I casted the spell that lets you bring out any creature from your deck. I brought out the Elf that lets you cast bring out a land when you play it. You should have 3 mana left to cast this creature and bring out the 8th and final Land.