15 cards where the mana value = 1 and the mana cost is not greater than or equal to {X} and the toughness = 0

Arcbound Mouser (Modern Horizons 2 #3)
Star Pupil (Strixhaven: School of Mages #30)
Vebulid (Urza's Saga #165)
Slag Fiend (New Phyrexia #95)
Evolving Adaptive (Phyrexia: All Will Be One #167)
Servant of the Scale (Dragons of Tarkir #203)
Simic Initiate (Modern Masters 2015 #162)
S.N.O.T. (Unhinged #111)
Spike Drone (Tempest #258)
Swarm Shambler (Zendikar Rising #207)
Traproot Kami (Betrayers of Kamigawa #147)
Zabaz, the Glimmerwasp (Modern Horizons 2 #243)
Arcbound Worker (Modern Masters #201)
Clockwork Beetle (Mirrodin #153)
Iron Apprentice (Kamigawa: Neon Dynasty #248)

This search is finished. Now the real work can begin.