2005-10-01
The first ability triggers when Golgari Brownscale returns to your hand from your graveyard for any reason, not just when you use its dredge ability.
2013-06-07
Dredge lets you replace any card draw, not just the one during your draw step.
2013-06-07
Once you decide to replace a draw using a card's dredge ability, that card can't be removed from your graveyard "in response." (Replacement effects don't use the stack.)
2013-06-07
You can't use dredge unless you're going to draw a card and the card with dredge is already in your graveyard.