Complex sentence: Meanwhile, Vegeta believes that Frieza is now immortal, but Kuririn points out that Freeza hasn't made his wish yet, because if Freeza had summoned the Namekian Dragon the sky would have turned black.
Split into simpler sentences: Meanwhile, Vegeta believes that Frieza is now immortal, but Kuririn points out that Freeza hasn't made his wish yet. Kuririn explains if Freeza had summoned the Namekian Dragon the sky would have turned black.