This gun is often thought to be the variated version of the Pain Hammer, since they both possess the same damage output. They also have a 'firery' paint job on their handles. However, the Pain Hammer is a credit weapon while Firewave is available for coins at Level 22. It can be bought permanent for 46,800 coins. The firewave also can jump boost you a tiny amount if fired onto the floor. However, the jump boost is gone since 4.3.
It's old price (starting from 4.4) is 1,400 for points and 6,120 for credits.
New price (4.5) 2,600 credits
This shotgun, along with the Ectopod and Thunderbuss, share the same "J"-type shotgun, in which the gun consists of a relatively heavy and bulky barrel, with an extremely thin handle at the back to hold. The aforementioned shotguns also use this frame, but have ben reskinned and re-balanced to become a new gun.
WARNING: Do not get directly in a players face when they possess the Firewave, as that would mean that all 168 units of damage would be absorbed by you. Unless you reccently picked up an UberHealth/UberArmour/or are wearing loads of armour, this is by all means fatal.