You can get random cards in Booster Packs or buy premade Starter Decks
The most restrictive thing about building with this combo is of course the deckbuilding restrictions that come with needing to support Blue cards alongside a card with mana cost BBBBBB
[expand title=Standard Dredge with Merfolk Secretkeeper (Arena Formatted Decklist)] 4 Discovery // Dispersal (GRN) 223 4 Arclight Phoenix (GRN) 91 4 Creeping Chill (GRN) 66 4 Drowned Secrets (GRN) 39 4 Opt (XLN) 65 17 Island (XLN) 265 4 Mission Briefing (GRN) 44 1 Maximize Altitude (GRN) 43 4 Radical Idea (GRN) 52 4 Watery Grave (GRN) 259 4 Unsummon (M20) 78 4 Merfolk Secretkeeper (ELD) 53 2 Selective Snare (GRN) 53 3 Mystical Dispute (ELD) 58 3 Disdainful Stroke (GRN) 37 3 Ashiok, Dream Render (WAR) 228 1 Negate (RIX) 44 3 Jace, Wielder of Mysteries (WAR) 54 2 Aether Gust (M20) 42 [/expand] Drowned Secrets is by far the most important card in this deck
Whispers in the Well investigates the source of a new location, the Inkwell Caverns, found below the Great Illuminary
Sai, Master Thopterist is the most flexible among legendary creatures with this play pattern, as there are plenty of strong artifact-centric strategies that synergize with its effects for building an army or drawing cards as the situation warrants
Target player reveals their hand