DEBUT: Omega Red, Darkstar, Illyana (aka Magik)
Omega Red said he was imprisoned for 25 years. He was frozen after the Russian government saw him as out of control. With the show broadcasting in 1993, this would have put his imprisonment at 1968. This would put it around the same time as the Warsaw Pact invasion of Czechoslovakia.
The on-screen coordinates Wolverine calls up for the location of Jubilee's plane indicate that Colossus's unnamed country is Kazakhstan, which became independent in December 1991 as a result of the USSR's collapse.
Gambit appears, but has no lines.
In the flashback scene with Wolverine fighting omega red, there's a glimpse of Captain America on the screen.