User blog comment:ReverseZoom101/"Crisis On Earth-X" Plotholes and Easter Eggs!/@comment-3127448-20171210072250/@comment-5441128-20171210073809

Well not all Kryptonians are nice and well mannered like Kara and Barry told about Earth 38 and Oliver saw how powerful Kara was in last year.

Cisco did make the Cold Gun because he thought Barry will be evil and then Savitar and the self destruct. Oliver could have asked someone on Earth to give him some Kryptonite from Earth 38. There are many other teleporters.