Complex sentence: Octopus and Floss's experimentation have led to the creation of a serum (something of a scientific equivalent to the Elixir of Life) that could grant immortality; after testing it on the murdered officer Colt, the Octopus injected himself and arch-enemies were born.
Split into simpler sentences: Octopus and Floss's experimentation have led to the creation of a serum (something of a scientific equivalent to the Elixir of Life) that could grant immortality. Eventually, the Octopus injected himself and arch-enemies were born.