You can't
In halo 3 the invincible item can only be found in the campaign and when you use it you will become invincible to gun fire but you can be: assassinated or fall to your death
At some points during the game there are equipment pick-ups that make you invincible. Brute Cheiftains carry these, so if you kill them before the use them you will get it. So yes, you can become invincible.
no it is not possible to be invincible in the campaign only in firefight and in custom game you can be invincible
Yes, if you pick up a custom power-up (yellow orb) whitch are not on default maps but only player created maps if the settings are correct you can become invincible
i do not think you can even get a worthhog invisible. you might but i doubt it.
If you meant to become invincible, there is a piece of equipment you can pick up in Campaign called Invincibility. It's dropped by Brute Chieftains and renders the user invincible for 12 seconds. The other way to become invincible is edit the settings in Forge or Custom Games. You can set your level of health, your recharge rate, your level of shielding, your ammo, your movement, and your damage. For health, damage, and ammo, you can set all of those to infinite if you so please.
halo 3 obviously
panda face 1 speed 4 size time invincible 3 pirate speed 2 size 3 time invincible 1 green skull speed 3 size 2 time invincible 1 eyeball speed 2 size 1 time invincible 2 planet earth speed 3 size 3 time invincible 2 mad face speed 4 size 2 time invincible 3
Halo 3: ODST is the newest of the two, but not the newest Halo game.
The halo time line goes Halo Wars, Halo: Reach, Halo:CE (halo 1), Halo 2, Halo: ODST, Halo 3. Halo 3 and ODST are practically at the same time.
Halo 3 ODST is not for PC but Halo 1 and maybe Halo 2-3 are
After Halo 3 there was halo wars, halo 3 ODST, and Halo reach. A new company (not Bungie) will be making a Halo 4 and rumor has it there will be a remake of Halo Combat Evolved.