Sanguine Spy

• WOTC Official Reminder Textofficial rules
  Surveil — Look at the top N cards of your library. Put any number of them into your graveyard and the rest on top of your library in any order.
• WOTC Official Reminder Textofficial rules
  Lifelink — Damage dealt by this creature also causes you to gain that much life.
• WOTC Official Reminder Textofficial rules
  Menace — This creature can't be blocked except by two or more creatures.

• WWizards of the Coast2022-04-29
  Official Ruling
  The mana value of a double-faced card in your graveyard is always the mana value of the front face.
• WWizards of the Coast2022-04-29
  Official Ruling
  X is 0 when determining the mana value of a card in your graveyard.
• WWizards of the Coast2022-04-29
  Official Ruling
  “Five or more mana values among cards in your graveyard” means there are at least five different mana values among those cards.
• WWizards of the Coast2022-04-29
  Official Ruling
  Sanguine Spy's triggered ability checks the number of mana values among cards you control both when the ability triggers and when it resolves. If you no longer have five or more mana values among those cards when the ability resolves, you may not pay 2 life.
• WWizards of the Coast2022-04-29
  Official Ruling
  The mana value of a split card in the graveyard is the total mana value of both halves of that card. It does not have two mana values.
• WWizards of the Coast2022-04-29
  Official Ruling
  The mana value of a land card is 0.

Rulings via Scryfall