Staff of Osiris
The Staff of Osiris is the main weapon of Horus and Isis in Lara Croft and the Temple of Osiris. It shoots a light beam that can kill any enemy. Additionally it is also the source of their shield. Furthermore it can be used to manipulate the surroundings that bear the Osiris Glyphs (like raising columns) and slowing down Time Bombs.
When not in Multiplayer mode, Lara also carries the Staff, because without it it would be impossible to end the game successfully.