Alien Capsules Book One has write ups on ten aliens ranging from nameless minions to deadly foes to potential allies. Each is ready to bedevil, support of mystify your players. Some can do all three. If your White Star or OSR game needs more extraterrestrials this is the mother lode. Each description includes full game stats for your alien as well as a setting agnostic background write up and some adventure hooks.
So if your adventure is lagging, have an alien with a gun walk into the room.