I've had halo 2 for years and never heard about the plasma rifle scarab gun... that is crazy! tempted to go get it now.
I would love to see the CE Pistol back, but i don't think it should have a scope as it would be more powerful than the battle rifle.
I was disappointed with the Halo 3 pistol not so much power and accuracy but the rate of fire. Its just too slow to do some real damage hence why I never see anyone use in online.
As for being hidden like the scarab gun, looks like we're gonna have to do some searching