Great Key

"Or maybe, it's a key all the time and when you stick it in people, it unlocks their death."

- Caboose in Under the Weather

The Great Weapon is an energy sword Tucker finds in a hole under the windmill in Zanzibar while the group tries to assassinate O'Malley. It is later revealed by Gary to be a relic of a long lost civilization.

Role in Plot
The Alien needed the sword to fulfill a prophecy to become leader of his race. At the end of a long quest, the sword is revealed to be a key to unlock the alien ship, which Tucker comments on "The sword is a Key? Just when I thought this quest couldn't get any lamer." After Wyoming kills the alien and busts the ship, Tucker and co. return to Blood Gulch where the sword becomes his main weapon of choice but he still pines for the sniper rifle. At the end of the season, Tex steals the sword and kidnaps Junior, because only he and Tucker can use it. When Andy blows up the ship they were on, it was believed to be destroyed.

At some point, Tucker was able to reclaim his sword and in the meantime acquired a great deal of skill with it, as he was able to use it to kill several of the "excavation team" members with ease, albeit off-screen, as well as timing the swings in order to completely destroy a warthog being driven by C.T. and cutting in half a giant crate thrown by Tex.

However, it can be assumed that since Gary lied, the great weapon may not be as great as the prophecy foretells. However, it is stated that the Weapon is a real alien belief, though this blade may have just been made by Wyoming and Gary as part of their plan to use the alien's beliefs against them.

Trivia

 * Tucker comments that "The sword is a key? Just when I thought this quest couldn't get any lamer." This line is probably a reference to the Kingdom Hearts series' unique weapon; the Keyblade.
 * The sword appears to have other functions, such as being a key to open a door to an alien ship and also allowed Tucker to retain his memory after having Wyoming's temporal distortion armor ability used on him.
 * Despite Tex apparently taking the sword with her on the ship in Why Were We Here?, Tucker seemed to have regained it when he returned in Well Hello.
 * In Lost But Not Forgotten, Caboose compares Tucker's sword to a lightsaber.
 * Xbox marketplace offers an Energy Sword Prop for your RvB Grif Avatar.