Deep Trouble is a race for lore, much like the standard format of play
But let's say you have a bunch of expensive cards and want to juice up these decks without testing them first
Silas Renn's color identity is blue and black, and Bruse Tarl contributes red and white
Maybe the connection is a creature type, or the cards play well together, or they have some story element in common

Arcane Bombardment Arcane Heist Arcane Proxy Arcane Savant Bloodthirsty Adversary Blue Mage's Cane Chandra, Hope's Beacon Chandra, Pyromaster Demilich Dual Strike Elemental Expressionist Elite Arcanist Emeritus of Truce Ether Eye of the Storm Finale of Promise Flawless Forgery Founding the Third Path Galvanic Iteration God-Eternal Kefnet Impulsivity Increasing Vengeance Isochron Scepter Jaya, Fiery Negotiator Magar of the Magic Strings Mizzix's Mastery Mnemonic Deluge Muddle, the Ever-Changing Myra the Magnificent Mysterious Stranger Panoptic Mirror Psionic Ritual Refuse // Cooperate Renegade Bull Roving Actuator Saruman of Many Colors Signature Spells Skycoach Conductor Soundwave, Sonic Spy Spellbinder Spellbinding Soprano Spelltwine Spellweaver Volute Stella Lee, Wild Card Storm of Memories Stormsplitter Surge to Victory The Tale of Tamiyo Wizard's Spellbook Wizards of Thay