Reiser will play Dr. Owens, a Department of Energy staff member who has been tasked with cleaning up the mess left behind at the end of season one.
Also boarding the new season is Danish actress Linnea Berthelsen, who will portray Roman, a damaged young woman with connections to the town and the research lab that jumpstarted the events in the first season.
The trio joins previously announced additions Sadie Sink and Dacre Montgomery, who will play siblings in the show’s sophomore run. Stranger Things fave Millie Bobby Brown will also be back as Eleven.
On Friday, Stranger Things kick-started production on the new season, sharing this upside-down tweet to commemorate the occasion.
Over the weekend, Stranger Things star Charlie Heatonteased the new episodes, hinting to ET that they are going to be “slightly darker” than season one and revealing that there will be a significant time jump.
"You follow these characters a year later, and you're straight back in the world of Hawkins, which we know and love so well,” Heaton explained. "The scope feels bigger this year."
Stranger Things will return in 2017.
For more on the new season, watch ET’s exclusive video below.