New power-ups: invisibility, quad-damage and defence

Introducing new power-ups: 

• Invisibility. Makes you almost invisible to the opponents(0.09 alpha channel). Lasts for 15 seconds. Respawns after 30 seconds.
• Defence. Absorbs 50% of damage.  Lasts for 10 seconds. Respawns after 35 seconds.
• Quad damage. Gives a 4x boost to shooting and punching damage. Lasts for 10 seconds. Respawns after 45 seconds.

And here is the gameplay video showcasing the power-ups:

A real 1-on-1 duel against my friend with the power-ups: