Speculating is the riskiest form of investing
They are primarily subdivided according to their frame color, into Normal Monsters, Effect Monsters, Fusion Monsters, Ritual Monsters, Synchro Monsters, Xyz Monsters, Pendulum Monsters, Link Monsters and Monster Tokens
Whether its a sideboarded Mirran Crusader, a pile of Lingering Souls tokens, an Etched Champion, a Young Pyromancer and company, a Nexus of the Blinkmoth or Inkmoth variety, fourteen 1/1 Goblin tokens, or simply a small pile of mana accelerants, Kozileks Return will clean them all up at instant speed, and theres no saving them with Burrenton Forge-Tender
Even that isn't too big of a concern, because players will often draw into other perfectly usable cards