21 cards where the color identity ≤ B and the card has the keyword “Proliferate”

Blightbelly Rat (Phyrexia: All Will Be One #85)
Carnival Elephant Meteor (Unfinity Sticker Sheets #7)
Contagion Clasp (Duel Decks: Mirrodin Pure vs. New Phyrexia #67)
Contagion Engine (Scars of Mirrodin #145)
Core Prowler (Mirrodin Besieged #103)
Drown in Ichor (Phyrexia: All Will Be One #91)
Everythingamajig (Unstable #147a)
Glistening Sphere (Phyrexia: All Will Be One Commander #20)
Grim Affliction (Modern Masters 2015 #84)
Gulping Scraptrap (Phyrexia: All Will Be One #96)
Karn's Bastion (The Lost Caverns of Ixalan Commander #339)
Recon Craft Theta (Fallout #141)
Scheming Aspirant (Phyrexia: All Will Be One #107)
Spread the Sickness (Modern Masters 2015 #98)
Staff of Compleation (Phyrexia: All Will Be One #242)
Sword of Truth and Justice (Modern Horizons #229)
Throne of Geth (Double Masters #301)
Vat Emergence (Phyrexia: All Will Be One #112)
Vraska, Betrayal's Sting (Phyrexia: All Will Be One #115)
Whisper of the Dross (Phyrexia: All Will Be One #117)
Yawgmoth, Thran Physician (Dominaria Remastered #110)

It is the moment of discovery, the triumph of the mind, and the end of these results.