All you need are a few Lego pieces and a lighter ignition plug.
Even the shock it weak, it still can startle people who are shocked by it.
It is a piece of quarts that gets pressurized till it generate electricity. Once there is enough energy the electricity fires out of the ignition ends causing the lighter light up.
Step 1: Legos
The pieces you need are:
-t-shaped connector (blue)
-2x 3long x shaped rods
-foot and leg from a bionical
-a x shaped rod connector
-1x 4 long x shaped rod
-circle to x shaped adapter
The rest just make it look like a gun.
Step 2: Wiring
Add extension wires to the ignition with tape or glue.
Run the extension the the aluminum tape.
Now connect everything and pull down on the trigger and see blue sparks arch across the 2 ends of the prongs.