There's no restrictions on stats, type, or mana value of the creature being brought back to the battlefield, and the only thing you have to give up to play it is the three generic, one white to play it
Cards that cantrip (draw a card for one mana) are also a vital part of the strategy
This could be the same bookcase and lines that the DuckTales nephews find in Might Solve a Mystery Or Rewrite History
A Clue is a colorless artifact token with the ability ", Sacrifice this artifact: Draw a card." So, as you can see, whenever a spell or ability tells you to Investigate, what you're really doing is making a Clue that can be turned into a card later
Switching from prison pieces to combo pieces means you deny opponents the chance to come back, but the prison decks are more flexible in putting together a win and can ride a single turn-one spell to victory