New heavy cannon prototype: Gravedigger

Gravedigger is a brand new heavy cannon prototype featuring freeze-inflicting shells and self-boosting capabilities. Landing 5, 15, or 25 multi-kills will supercharge its next shot, dramatically increasing damage and blast radius, and at the final threshold, deploying a force-pulling proximity mine. Refining the Gravedigger unlocks increased damage, faster firing speed, and easier supercharges by lowering the multi-kill thresholds.