The Shock Wave

o Spy melee weapon
o Custom particles
o Jiggling strap
o 4 LODs

Additional concept by Jericho
Custom particles by Chaofanatic

Feel free to suggest other names and discuss about weapon stats.

Some gameplay ideas:

a) Kill enemy players using the Cow Mangler death animations
b) No backstabs, disables enemy's primary and secondary weapons for a few seconds forcing a switch to the melee weapon. Maybe also affect other nearby enemies so you can tackle a whole group. Just like the Razorback mechanics only that it disables the enemies' weapons within a certain radius.
*) Disable enemy buildings for a few seconds
*) Does not work in water
*) Drains the cloak meter on use
*) Takes a few seconds to re-charge
*) Emits electric humming sounds while not cloaked
*) Does additional damage to all players connected to the victim by a healing beam

It could be a simple knife replacement using the Cow Mangler death animations. The second idea instead might work as an alternate play style. Hitting an enemy disables his primary and secondary weapon (like the Razorback does with the knife) for a few seconds and automatically switches to his melee weapon. The Spy's weapon is automatically switched to the revolver slot since it takes the Shockdown some time to re-charge. The weapon disabling also applies to other nearby enemies (and possibly buildings?) within a certain radius.