Hogwarts: Nagini captured at the start

Robin is transported to a Western magical world and gains a cheat code—the Magical Creatures Breeding Cube!
Once you defeat a magical creature, you can collect it into the cube. You can also improve its magical attributes and combat power through a series of feeding and nurturing processes.
Nagini venom is too weak; it only causes wounds to bleed uncontrollably.
Garden goblins are so useless; all they do is dig holes and gnaw on roots.
The Black Lake mermaid is ugly and can only lure people to drown with her singing.
The roots of the "Hit-Man Willow" are deeply embedded in the ground, making it only suitable for close-range attacks.
The Hungarian Horned Dragon is enormous but has limited vision, making it ineffective in close combat.
......
When the second Dark Lord led his forces to attack, he was shocked to find that Hogwarts had become the headquarters of magical creatures.
Then, he and his men were beaten so badly by the mutated creatures that they couldn't even find their way north!