In Board Game Island, an UFO comes when a player steps on an UFO space. A die roll determines who will change places with him. Then the UFO comes, absorbs the two players and drops them on each other's squares. The player can't change places with another player in the volcano or on the same square.
In Globe Trot, when a player steps on a Surprise spot, there can be a single UFO (change place with another player) or an UFO Armada. The UFO Armada consists of 4 UFOs, absorbing the four players and throwing them down at random places.
In Saucer Snap, the goal is to take a picture of an UFO as it quickly goes by. The player who gets it closest to the centre wins.
In Space Brawl, space objects, including UFOs, can be thrown at each other for points.
In Lofty Leap (aka Rope Sling), if the player leaps high enough, they will go into space, where there's an UFO.
In the challenge version of Shifty Gifts, UFOs can sometimes appear.