Thought-Knot Seer [Oath of the Gatewatch Prerelease Promos] Dragon Avatar Tawnos finally cracked the puzzle:

Tawnos finally cracked the puzzle: the strange structures did not house Mishra's malevolent creations but were themselves among his creations

slaying the unworthy

you may put Nether Shadow onto the battlefield

Mishra also mastered the intricacies of artifice

Thought-Knot Seer [Oath of the Gatewatch Prerelease Promos] Dragon Avatar Tawnos finally cracked the puzzle:Set: Oath of the Gatewatch Prerelease Promos Type: Creature Eldrazi Rarity: Rare Cost: {3}{C} ({C} represents colorless mana.) When Thought Knot Seer enters the battlefield, target opponent reveals their hand. You choose a nonland card from it and exile that card. When Thought Knot Seer leaves the battlefield, target opponent draws a card.