Thought-String Analyst is a rare Creature — Human Wizard card from Alchemy: Murders at Karlov Manor (YMKM), collector number 29.
At the beginning of your upkeep, exile the top card of target opponent's library face down. You lose life equal to its mana value. You may look at and play that card for as long as it remains exiled, and mana of any type can be spent to cast that spell.