The Arrowverse "Invasion!" crossover has come to a close, but the door remains open for more crossovers in the future. The Flash, Arrow and DC's Legends of Tomorrow all exist in the same universe, while Supergirl resides in a different part of the multiverse on Earth-38. But the conclusion of the "Invasion!" crossover added a new wrinkle that makes bringing Supergirl into the fold a lot easier in the future. Full spoilers for the "Invasion!" crossover continue below.