A cannon that made out of 3 iron and a sign on the back the states [cannon] and a redstone torch on the last iron block when you leftclick it turns the cannon 90* and it can shoot an arrow or snowball and it shoot straight and it explodes when it hits something not water or air and it can blow stuff up underwater IB = iron block S = sign RT = redstone torch RT S,IB,IB,IB
Sealteam108 Bukkit's super simple just learn it. If you know Java then you can learn what you need of the Bukkit API and get this done in under an hour. That is, if you actually do know Java...