This build essentially replaces most of the creatures in your deck with as many copies of Rat Colony as you want to include

Acrobatic Leap Act of Heroism Ahn-Crop Champion Ajani Vengeant Alarum All-Out Assault Angel of Condemnation Arbalest Elite Augusta, Dean of Order Aurelia, the Warleader Aurelia, the Warleader Axgard Braggart Ballynock Trapper Barrenton Medic Basil, Cabaretti Loudmouth Basri, Tomorrow's Champion Battle Cry Bazaar Krovod Beacon Hawk Betor, Kin to All Blessed Alliance Blinding Beam Brightfield Mustang Burst of Energy Call to Glory Captain America, Living Legend Cat-Owl Catch // Release Celestial Regulator Companion of the Trials Crackdown Damping Field Dauntless Aven Dazzling Theater // Prop Room Dazzling Theater // Prop Room Deepchannel Duelist Deepway Navigator Defiant Stand Deftblade Elite Derevi, Empyrial Tactician Devoted Crop-Mate Dihada, Binder of Wills Djeru's Resolve Dovin Baan Dovin, Architect of Law Drumbellower Duergar Mine-Captain Elite Interceptor Energy Arc Energy Storm Enshrouding Mist Entangling Trap Equipoise Escape from Orthanc Esper Sojourners Essence of Antiquity Estrid, the Masked Famished Paladin Fancy Footwork Finest Hour Flash Thompson, Spider-Fan Flying Crane Technique Gauntlets of Light Gerrard's Command Gideon, Battle-Forged Gideon, Martial Paragon Gleam of Resistance Glory-Bound Initiate Granite Witness Gust Walker Gustcloak Cavalier Gustcloak Harrier

You may cast an instant or sorcery spell from among them without paying its mana cost
You can also use cards like Brutal Hordechief and Commissar Severina Raine to push damage while attacking
Undead Augur Undead Augurs in that same category as the 3-drop card advantage creatures, but its a 2-drop, and is actually relevant for a certain black devotion wincon