First Flash episode to air on Sunday. Ralph even notes (as a breaking the fourth wall in-joke) that it's "not even Tuesday," a reference to when the show actually airs, as it swapped time slots with Supergirl (2015) for the Elseworlds crossover event.
Heroes identified in the 'cold open' Earth 90 scene are: Flash, Monitor, Star Girl, Green Arrow, Hawkman, Hawkgirl, Obsidian, Huntress, Firestorm, Captain Cold, Jesse Quick, and The Ray.
After Barry and Oliver switch places Barry refers to it as a Freaky Friday situation before deciding it's more accurately a Quantum Leap. In the Freaky Friday movies the characters minds swap bodies. In Quantum Leap Dr Sam Beckett changes places with people where he's still in his own body but people perceive him to be the other person, which is closer to their situation.
When Barry shoots Oliver with arrows it's almost an exact replica of the original scene from "Flash vs. Arrow", with Barry and Oliver switching dialogues and roles. The shot that shows the remote control bows is recycled from that episode, with only a few changes through edits.