Complex sentence: After Catlin tells him about a weapon created by Dr. Light, he uses it on Deathstroke to stun him so that they can run and get help, though help comes too late as he finds what he was looking for and leaves.
Split into simpler sentences: After Catlin tells Cisco about a weapon created by Dr. Light, he uses it on Deathstroke to stun him so that they can run and get help. Help comes too late as Deathstroke finds what he was looking for and leaves.