You've seen the "crane games" the UFO catchers before I'm sure. As I remember when I was young at amusement parks and arcades and such, I would see stuffed animals and candy and try tirelessly to get what I wanted.
Japan has taken the "UFO catcher" addiction to new heights with dedicated areas in most arcades, and outside many shops to lure you in with bright colorful prizes. It looks very easy, which is exactly what pulls you into this addicting activity.
However, the system can be beat with a little bit of patience and skill, and from what I've seen, UFO prizes can be a very good souvenir to bring back home, as many times the prizes in these machines cannot be purchased anywhere else.
If you think you have the skill, you could spend an entire day in the downtown areas visiting different arcades, trying to get the best UFO prizes. Stuffed animals, keychains, electronics, snacks, accessories are just the beginning, so get out there and have a UFO adventure! But be sure to set a budget, because your money may be gone before you know it!
Check this guide for a bit of strategy: