The Red Solstice currently has many different damage types:
Physical Damage is utilized by the vast majority of zombies. The only current exception to this are the bloppers.
Hollow Point damage originates from Hollow Point ammunition.
In general, Hollow Point tends to be more effective against early wave enemies than late wave enemies.
Swarmers, Ghouls, Zombies, Stalkers, Blood Hounds, Behemoths, Lyganesh, Leviathan are more vulnerable to Hollow Point Damage and are resilient towards Piercing Damage.
Piercing damage originates from the Full Metal Jacket ammunition. In general, Piercing tends to be more effective against late wave enemies than early wave enemies.
Flesh Beasts, Fiends, Devourers, Bloppers, Slashers, and Fluffies are more vulnerable to Piercing Damage and are resilient towards Hollow Point Damage.
Seismic damage originates from the Seismic Resonator item and the demolition's Seismic resonator device. Enemies killed by Seismic damage do not revive.
Bloppers, Mini-bloppers, and the Hatchling are currently the only enemies that utilize toxic damage. Toxic Barrels and the Toxic grenade are the only current player sources of toxic damage.
There are no known enemy sources of energy damage aside from the insurgent leader Nyx.
Explosive damage originates from explosive bombs, grenade launchers, rocket launchers, and the Shiva.
Explosive damage can set off placed explosives.
There are no known enemy sources of explosive damage.