The Alien was the top of the line MTB for Nishiki that year. The bike you're looking at has the rounded tubing that I believe is steel. In 1990 through 93, the Alien had box/rectangular tubing and was made of aluminum. The later Aliens still bring nice bucks on ebay if you can find one with the headtube not cracked. The steel model was downgraded to the second place model in the 1990 line-up. The Ariel and the Cascade shared the steel frame.
If you add a nice suspension fork and some decent brakes, like V brakes those elevated chain stay bikes make great rides on single track as they have great handling charachteristics, very stable. I compared mine directly to a same vintage (1992) Trek 8500. The Trek had a superior Rock Shox air fork but couldn't come close to the handling of the Nishiki. Here's a pic I took last year out at Harris Lake park of my 92 Ariel. Note how similar it is to the 89 Alien. I believe the frames are identical.
