You can hike to Marial from either Grave Creek or Foster Bar. Marial is accessible by car/truck via the Mule Creek/Marial rd. Rather than explain this leg of the aforementioned long shuttle, I'll just say that it is a good ways in on a low elevation slide prone road from the coastal end. Not sure I'd recommend it, especially beyond Illahee. From Grave Creek, the MC/M rd. climbs to over 3000 feet and is prone to slides and snow. Not sure if it is even open from that end in winter and definitely would recommend against it.
The Grave creek TH is the most convenient access. The TH is at around 700' ASL and its terminus at Foster Bar is at around 500' ASL. With the exception of a few switchbacks near Grave Creek and between Clay Hill and Foster Bar, the trail is at a constant gradient. Other than possible winter slides and blow down, it is a mild trail.
Options are: Two cars, one at either end with the long shuttle, one car with a paid shuttle from Grave Creek to Foster Bar, or start at Grave Creek and pick a spot to turn around and hike back up to the Grave Creek TH.
Trail mileages by main lodges:
Grave Creek to Black Bar is around 10 miles, Black Bar to Marial around 15 miles, Marial to Paradise around 5 miles, Paradise to Illahee (Foster Bar) around 10 miles.