Mulbah joins the Mountaineers with three years of eligibility remaining.
The Nittany Lions are ranked as high as No. 4 in the country in some "way too early" top 25 polls.
Jahan Dotson, Saquon Barkley, and Miles Sanders all scored touchdowns during week 13 of the NFL season.
Miles Sanders had a career day for the Eagles with 143 rushing yards and two touchdowns on Sunday Night Football.
Robinson will undergo surgery and miss the remainder of 2022 season.
Penn State finishes the year 17-4 with a share of the Big Ten regular season title.