Mission Creek Pkwy is a very old doubletrack multi-use trail. Some parts of this trail follow what was once (circa. 1928?) built by the WPA to be a 'road' which was never fully realized, and other parts follow a historic railroad grade. The track itself can be pretty rough, but it's wide. This doubletrack trail is important to the Mission Creek mountain bike singletrack cluster (and the Duluth Traverse) because it intersects and connect several existing (and future/planned) singletrack segments of the system, and it also provides an "opt-out" option.
The grade is fairly tame overall, but starting from the south (heading north) you'll initially descend until you get to Mission Creek, then it's a gradual climb the rest of the way up to Beck's Rd (Highway 3).
There are several river crossings along the way: some have stone bridges (vestiges of the WPA 'road' project?) but there are a handful of other crossings where the bridge is long gone and you have to shoulder your bike and rock-hop or wade through (water level fluctuates seasonally / usually shin-deep).