Moldervine Cloak

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.

Dredge can replace any card draw, not only the one during your draw step.

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.