Grave-Shell Scarab

• WWizards of the Coast2005-10-01
  Official Ruling
  You may sacrifice Grave-Shell Scarab to pay for its first ability, then replace that draw using the Scarab's dredge ability. The result is that the top card of your library is put into your graveyard and Grave-Shell Scarab returns to your hand (after a brief trip to the graveyard).
• WWizards of the Coast2024-01-12
  Official Ruling
  One card draw can't be replaced by multiple dredge abilities.
• WWizards of the Coast2024-01-12
  Official Ruling
  You can't attempt to use a dredge ability if you don't have enough cards in your library.
• WWizards of the Coast2024-01-12
  Official Ruling
  If you're drawing multiple cards, each draw is performed one at a time. For example, if you're instructed to draw two cards and you replace the first draw with a dredge ability, another card with a dredge ability (including one that was milled by the first dredge ability) may be used to replace the second draw.
• WWizards of the Coast2024-01-12
  Official Ruling
  Dredge can replace any card draw, not only the one during your draw step.
• WWizards of the Coast2024-01-12
  Official Ruling
  If an effect puts a card into your hand without specifically using the word "draw," you're not drawing a card. Dredge can't replace this event.
• WWizards of the Coast2024-01-12
  Official Ruling
  Once you've announced that you're applying a card's dredge ability to replace a draw, players can't take any actions until you've put that card into your hand and milled cards.

Rulings via Scryfall