To make your sim a:
-Vampire: To become a vampire you have to go to..er..i forgot what it was called, but you have to go to the Gothic looking club at night. Then you just have to wait around until you see the head vampire. [Shouldn't be to hard; pale skinned, dark-haired man/woman dressed in medieval Gothic like clothing, walking around, crouched slightly with their arm over their face]. Once you find them, you have to get your relationship high enough [forgot how high] until you get the option to ask them to bite you, or they end up biting you on their own. [srry its been a while since i've played nightlife] Then, Boom!!, your a vampire :D
-Werewolf: To be a werewolf, you first need to have a wolf with glowing yellow eyes [the leader of the pack] to bite you. Just plant a whole lot of trees around your house, and he will come. Just like the vampire, you relationship needs to be high enough with the wolf, for you to get the option for them to bite you, and then your a werewolf.
-Plantsim: This I heard from a website, it sounds easy, but i have never achieved it. All you gotta do, apparent;y, is use pesticides on all your trees and plants when they get infested with bugs. And you gotta do this alot, and all the time, all the time, all the time, until the chemicals turns you into a plant person. APPARENTLY!! I have never tested that theory, but i've heard it from a lot of different websites, so it should work.
-Robot: This one is the simplest; you can't make your sim into a robot, but you make them. All you need is to have a golden badge in robotics, have the robot building thing, and make one all on your own. :D Sims can marry the robots and the robots can marry other robots, and im pretty sure, that a robot and a sim can have a baby. o-o
To see:
-Ghosts: You need to have a tombstone. Then usually, I've had it every night almost, a ghost should come from it at night. Then all you gotta do is have your sims around the ghost until the ghost decides to scare that sim. [The only downside to this, is your sim can die of fright after seeing the ghost].
-UFOS: Buy a telescope and have your sims gaze into the stars at night a lot, for long periods of time. Eventually, and randomly, a event video will come up and you will have your sim abducted by the aliens. I've heard that if a male adult sim gets abducted he can get pregnant with an alien baby <3. But its only the man, not the woman,and again im not so sure...haven't tested that theory out yet :P But if you do gaze up at the stars with a telescope you will eventually get abducted.