Frankenstein's monster

noun2

1. •
   (figurative) A creation that overpowers or slips out of the control of its creator, often proceeding to turn on its creator or harm others.

   • They created a Frankenstein's monster which they did not imagine could grow out of their control. — 1968
2. •
   (figurative) A thing that is cobbled together from parts of other things.

   • Like the English language, the eukaryote cell is a chimera, a Frankenstein's monster, assembled from bits and pieces of genetic information... — 1991