On campaign it would be the scarab gun, it's a hidden gun that only appears on a few of the levels, and is very hard to get. The link below gives you an address for a site with the location. It has huge range, is very acurate and is the most powerfull weapon ever. It also never reloads, overheats or runs out of ammo. It has a continuous stream of energy, but watch out. The splash damage is immense, so if it hits near you, your dead. Here's the link: www.halo.wikia.com/wiki/scarab_gun Other than that you'll have to work it out for yourself!
it depends on what level you play, if on a level fighting flood the best wepeon is a shotgun or energy sword
the semen shooter
any weapons can be used even dual weapons
No you cannot duel wield and no bubble shields etc. or radar it truly makes it a different game play.
You can, one involves pickup a Dual-Wieldable weapon and support weapon simultaneously and another involves a Dual-Wieldable weapon and an Objective such as a Flag, a Bomb, or the Oddball. There are a lot of videos on YouTube that explain this very well.
No.
Custom Lego Halo weapons can be found on sites like eBay and Firestar.
343 Did not make dual wielding a feature.
Anything with a large spread or most of the plasma weapons
You can not dual wield energy swords in halo 3 but there are rumors that you can in halo reach.
Buy Daggers, they are dual wield.
ebay
no
no there are no "cheats" in halo, thought many glitches