Complex sentence: Drug lord Peter Rooker has allied with a scientist who also worked on Darkman's super-strength and invulnerability; he has invented a steroid that gives test subjects super-strength, but leaves them mentally unstable.
Split into simpler sentences: Drug lord Peter Rooker has allied with a scientist who also worked on Darkman's superhuman strength and invulnerability. He has invented a steroid that gives test subjects superhuman strength, but leaves them mentally unstable.