Complex sentence: Maxwell Lord arrives and admits to creating the synthetic kryptonite, though he states it was originally meant to be used against Non and his Kryptonian army and Kara's infection was an accident, and offers to help create a antidote.
Split into simpler sentences: Maxwell Lord arrives and admits that the substance was a synthetic kryptonite originally meant to be used against Non and his Kryptonian army. He explains that Kara's infection was an accident, and offers to help create a antidote.