The Scorcher is a powerful shock weapon that does just as much to cloud the enemy's vision as it does to deal damage to them. Throughout the campaign, you'll find Flame Grenadier and Flame Boomer that will carry these and use them against you. At first, it may seem weak compared to your other weapons but it is just a matter of being close enough as the maximum effective range of the weapon is quite short.
Aside from the normal use of burning things, the Scorcher also plays an important role in combat against the Berserker. You'll need to apply the Scorcher to weaken the outer armor of the Berserker before you can kill it.
