A wide variety of decks represent the Modern meta in Magic: The Gathering, running the gamut from Esper control decks and the tricky Death & Taxes build to aggressive blue Merfolk decks. Midrange decks are popular too, and one of them is called Dredge.
As the name suggests, this deck makes use of the Dredge mechanic, which dates back to 2005's Ravnica: City of Guilds. The Dredge deck uses all colors but white to rapidly develop an aggressive, death-resistant board state that can keep assaulting the opponent until they're ground down. This deck can also make good use of card advantage by bringing back creatures from the graveyard multiple times.
The Creatures Of Dredge
This is a creature-heavy deck, and a variety of blue and/or black creatures can fuel and benefit from Dredge's graveyard engine. Golgari Thug appears as 3-4 copies, a little 1/1 that is most valued for its Dredge 4 ability. It can chump block, but more often, it's used to mill its owner for four cards and fuel the graveyard even faster.
That leads right into the next creature, Narcomoeba, which typically appears as a playset. It's an evasive 1/1 that can be put onto the battlefield for free at unexpected times, synergizing wonderfully with Dredge abilities. Stinkweed Imp is a 1/2 flier with pseudo-deathtouch, costing 2B and having a whopping Dredge 5. Dredging that back is likely to get a Narcomoeba into play with zero mana being spent.
Other creatures in this deck can really make use of all these cards going into the graveyard. Bloodghast can get milled, then come back onto the battlefield each time Landfall is triggred (which is easy with fetchlands). It might even have haste. Prized Amalgam can tag along when Bloodghast comes back, and getting a recurring 3/3 beater for zero mana is the height of efficient. Even if the Amalgam eats a Lightning Bolt, it can come right back along with Bloodghast or Narcomoeba before too long.
A more recent addition to this deck is the mighty Ox of Agonas, a red mythic from the Theros: Beyond Death set. It has the Escape ability for RR and exiling eight other cards from the graveyard. Its 4/2 body is augmented with a +1/+1 counter when it escapes. If that weren't enough, this Ox can make its owner discard their hand and draw three cards, fueling the graveyard while refreshing their hand. If that Ox escapes, Prized Amalgam will come along, too.
Last up is Merchant of the Vale, a 2/3 from the Throne of Eldraine set. For just R, it can go on an adventure and rummage one card (discard, then draw), and as a creature, it can pay 2R and discard a card to draw a card.
Spells & Lands
Creatures are the star of the Dredge deck, but this build still needs support spells to realize its full potential, and noncreature cards can have the Dredge ability too. Life From the Loam is a must, a cheap green sorcery that can retrieve lands from the graveyard (such as fetchlands) to fuel Bloodghast's Landfall ability. It also has Dredge 3. Meanwhile, Conflagrate is more efficient when cast from the graveyard, costing RR and discarding X cards to deal X damage divided among any number of targets. It can be used to finish off the opponent, or get rid of troublesome creatures.
Creeping Chill is typically milled away, and when that happens, it's efficient, like a Lightning Helix to the opponent. Cathartic Reunion, a cheap red spell from Aether Revolt, greatly fuels this deck by requiring the caster to discard two cards, then draw three. Darkblast might be added too, costing just B to give a creature -1/-1, and it has Dredge 1.
This deck's manabase is complex and somewhat greedy. Fetchlands and shocklands in blue, black, red and green may all appear, not to mention fastlands such as Copperline Gorge and Darkslick Shores. A few basic lands might be added too, and Dakmor Salvage is sure to appear. It can tap for a black, or simply dredge for two if it got milled. Blast Zone might be added as a one or two-of to wipe the board.
Sideboard Options
Overall, Dredge decks are cautious about using a lot of cards from their sideboards, since they can't afford to dilute the graveyard/milling engine too much. Still, some problematic enemy decks demand answers, and Dredge has them. Lightning Axe can take out large enemy creatures such as Tarmogoyf, and discarding a card is a small price to pay for this spell.
Thoughtseize should work well against control or combo decks such as the Ad Nauseam deck or even Scapeshift decks, and Nature's Claim will wipe out troublesome artifacts or enchantments such as Expedition Map, Chalice of the Void (if it's not set to one) or Ensnaring Bridge. Alpine Moon can neutralize a Tron land to slow down mono-green Tron decks, or a problematic man-land such as Celestial Collonade. Finally, Dredge might also side in Abrupt Decay or Leyline of Sanctity for protection from dedicated Burn decks, though getting it in the opening hand is essential.