15“The Scientist” (2x08)
It’s no coincidence that the lightest episode in Arrow’s entire run just so happens to be Barry Allen’s Arrowverse debut. Pre-lightning bolt Barry is a bumbling mess, always turning up late and way too young to be investigating anything, which is referenced several times by Oliver: “Do your parents know
The humor in “The Scientist”, between Oliver’s snarky remarks and Felicity’s approval of Barry, does just enough to distract from the introduction of metahumans and super soldiers to a show that was once so grounded. The League of Assassins also gets a mention, as Moira brilliantly gets one over on Malcolm Merlyn in the background.
The episode uses Barry Allen to very subtly embrace its wider universe, but at the same time remains grounded as Mirakuru soldiers begin to surface in the present.