Resonance Disc

The Resonance Disk is an item introduced in Risk of Rain 2 The item grants charge on kill, and when full, fires a projectile dealing 300% damage, while also piercing enemies. Afterwards, it creates an explosion dealing 1000% damage, ending with the original projectile flying back towards the user, dealing 300% damage along the way. Initial code dive suggests that a kill gives 2.5% charge, and that charge decays at 1.25% per second.

Trivia

 * Resonance Disc is Risk of Rain 2 equivalent to the Risk of Rain 1 item, Laser Turbine