The Energy Sword is an alternative to the Shotgun as a short ranged weapon. It has a melee attack which deals the same amount of damage as the regular attack.
When the player uses the initial attack, the player is shown as pulling the sword back and a red and white "shield" is surrounding him/her, as if gathering up energy for a stronger attack, hence the name "Energy" Sword. Note that the "shield" is not an actual shield, as it is used for effect for the "energy" being gathered. When enough "energy" is gathered, the player attacks with a powerful swipe along with a large thrust forward. When used in air, it still does the above, but in addition the player's fall is slowed down. The Energy Sword is perfect for getting to hard to reach places, like when without the sword, jumping from a platform to another may fail. However with the Energy Sword, if they fail, they can power up the sword, and if aimed and timed correctly, the player can get back to the platform he/she was trying to reach. The Energy Sword cannot be used in air as the player cannot "regenerate power" while in air.
The energy sword also has the ability to deploy a sentry using its alternate fire, if enabled. It can withstand two zombie lunges, and deal considerable damage, but turns slowly. It is best used for area denial and fire support.