FATMAP difficulty grade
Fred's Lunch to Lion Down forms an upper intermediate descent all the way down the mountain, but the singletrack here is not downhill-specific.
Rather, this is a two-way trail that is meant to be either climbed or descended. Vail Mountain says that this "classic singletrack mixes tight, wooded sections with open meadows." As a result of the classic nature, this descent from the top of the lift is actually a bit tricker than some of the other trails in the Vail Bike Park.
Roots, rocks, loose sections, and abrupt corners make for a less predictable ride quality, as compared to trails like Big Mamba.
In fact, some would argue that this makes Fred's Lunch an even more enjoyable and worthy ride than many of the dedicated downhill trails in the Vail Bike Park. Sources: https://www.vail.com/explore-the-resort/activities-and-events/summer-activities/mountain-biking.aspx