Not one, but TWO games in the infamous Mortal Kombat series are in the works for Nintendo's handheld.
Today Midway released a huge new release schedule, much of it unchanged from the last time they did so. However, there were some new GBA games on there, including Ultimate Mortal Kombat for a Q1 2002 release, and Mortal Kombat 5 for a Q3 2002 release. MK5 has already been confirmed for GameCube and will come out approximately the same time...perhaps they'll link up?
Ultimate Mortal Kombat is most likely a port of Ultimate Mortal Kombat 3, which graced the arcades and a few home systems in the mid-90s. Hopefully we'll have some screens and further info on it very soon.