Glarb, Calamity's Augur

• 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
  Deathtouch — Any amount of damage this deals to a creature is enough to destroy it.

• WWizards of the Coast2024-07-26
  Official Ruling
  If the top card of your library has in its mana cost, you must choose a value of X that makes that spell's mana value 4 or greater in order to cast it.
• WWizards of the Coast2024-07-26
  Official Ruling
  If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so. This means that if you cast a spell from the top of your library, you can't look at the next one until you're done paying for that spell.
• WWizards of the Coast2024-07-26
  Official Ruling
  You can look at the top card of your library whenever you want (with one restriction; see below), even if you don't have priority. This action doesn't use the stack. Knowing what that card is becomes part of the information you have access to, just like you can look at the cards in your hand.
• WWizards of the Coast2024-07-26
  Official Ruling
  You must pay all costs and follow all timing rules for lands played and spells cast from the top of your library this way.

Rulings via Scryfall