Tonight saw the conclusion to the 4-part DC TV Invasion crossover which had a rather super cool Brandon Routh Superman Easter Egg.
The end of tonight's episode saw the DC TV heroes celebrating, with Supergirl back to her Kara Danvers self. As she walks away, Ray Palmer (Brandon Routh) says she looks a lot like his cousin.
This is a nod to Brandon Routh playing Superman in 2006 with Superman Returns (as Superman and Supergirl are cousins).
Producer Marc Guggenheim offered the following to IGN about the Superman reference:
Basically, it’s sort of like last year on Legends we did the Prison Break [reference], it was like, I said to the writers, ‘If we don’t make a Prison Break joke here with Wentworth [Miller], we’re not doing our jobs.’ I was like, “If we have Brandon [Routh] and Melissa [Benoist] share the screen and we don’t make some sort of joke like that, we’re not doing our job.’ The truth is, that joke existed on Arrow originally and then a certain scene got cut so then I moved it over to Legends; I just kept moving it back and forth. I’m like, ‘I’m getting it in one of these episodes.