Golgari Grave-Troll enters the battlefield with a +1/+1 counter on it for each creature card in your graveyard.
1, Remove a +1/+1 counter from Golgari Grave-Troll: Regenerate Golgari Grave-Troll.
Dredge 6 (If you would draw a card, instead you may put exactly six cards from the top of your library into your graveyard. If you do, return this card from your graveyard to your hand. Otherwise, draw a card.)
10/1/2005 If an effect puts Golgari Grave-Troll onto the battlefield from your graveyard, Golgari Grave-Troll counts itself as one of the cards in your graveyard and gets a counter accordingly.
6/7/2013 Dredge lets you replace any card draw, not just the one during your draw step.
6/7/2013 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.)
6/7/2013 You can't use dredge unless you're going to draw a card and the card with dredge is already in your graveyard.