Shroud is the mask Matt Trakker wears in the first Goliath, the racing car that anchors the Series 3 and the second-season race episodes. The fan wiki says it creates an inky black fog to confuse opponents, Wikipedia’s list says a temporary fog, and Matt-Trakker.com says it creates darkness, so the sources agree on the effect and differ only in whether it is a fog or an absence of light.
It belongs to the racing period of the cartoon. The fan wiki lists it in Where Eagles Dare, The Battle of the Giants, Challenge of the Masters, For One Shining Moment and High Noon, which is to say the stretch of the second season where V.E.N.O.M. and M.A.S.K. settle their quarrels on a racetrack.
Kenner packed Shroud with Goliath in 1987, alongside Matt Trakker and Nevada Rushmore, who carries the Totem mask for the second driver’s seat. Brad Turner’s Eclipse does nearly the same job for Razorback, and the wiki points out the likeness between the two.
