A harpoon is a spear that is usually thrown or thrusted. It is typically used for fishing, but can be used as a weapon. Any weapon could be used as a fishing tool. Shotguns? Sure. Assault Rifles? Why not? Would they be very effective? Not really.
Not 100%, but teleportation does exist on a very small scale: http://content.time.com/time/health/article/0,8599,1874760,00.html
Yes, but as far as weapons go, I don't think we need one that doesn't sound like or look like a regular weapon.
I just wanna chime in here, and point out that using the harpoon as an example for weapons needing to ALWAYS be serious, is a terrible idea... Here's why: In a game all about killing people while trying to not get caught (for the most part), as well as being filled with guns and explosives, with some weapons used for stealth, giving use to knives, a very large, pointed metal rod, used to throw at people sending their bodies flying, while either shouting, "THIS, IS, SPARTA!" or that yell from what sounds like Tarzan or George of the Jungle, is ENTIRELY ridiculous... I mean, come on, see this as evidence that sometimes, you NEED something ridiculous in a serious environment to stop you from taking it TOO seriously... Another prime example of how not EVERYTHING that is a weapon must be serious for those of you using the serious thing as why this shouldn't be a weapon at all: Jihad Sounds.... Don't even TRY to say this fits the "serious requirement"...