The episode in question is titled “Providence” (the eighteenth of the series), and the little Easter egg revolves around the character Marcus Daniels.
On the show, Daniels was played by actor Patrick Brennan, and is featured as a Darkforce-powered stalker of Audrey Nathan – the Portland-based cellist and former flame of Agent Phil Coulson’s who is first mentioned in Joss Whedon’s The Avengers.
He is a one-off villain from Agents of S.H.I.E.L.D., and has not yet returned since his first appearance, but an Eagle eyed fan has gotten confirmation that Marcus Daniels a.k.a.
Blackout has a small role in the 1990s-set Captain Marvel.