Dredge is best described as a midrange deck with combo elements. Against interactive decks Dredge generates card advantage with recursive threats, while interacting with the board thanks to Conflagrate. It is described as having combo elements because of the occasional fast draw it can generate when it finds its Prized Amalgams quickly. How powerful Dredge is at any given point is often related to how much graveyard hate people are playing. If you can dodge seeing cards like Rest in Peace and Leyline of the Void, this deck is very good. You can read more about Dredge on Star City Games here and here.
This is considered one of the boogie men of the Modern format because it tends to have fairly skewed match ups. Tron beats up on midrange and control decks, while struggling against aggressive and fast combo decks. If you enjoy playing big spells this is the deck for you. You can read more about Tron on Star City Games here.
Ulamog, the Ceaseless Hunger
Emrakul, the Promised End
This is simply a collection of reasonably powerful Modern-legal cards. Just some of the best spot removal, discard, and threats the format has to offer. It packs it all into a brutally efficient curve that allows it to easily keep up with the slew of linear decks that tend to see play in Modern. You can read some of my fuller thoughts on BG Rock on Gathering Magic here as well as some specifics on sideboarding with the deck here.