Hello and welcome back to your favorite suggestion guy. Now this suggestion is going to be trying to flesh out both realistic, fantastical, and quasi-magical elements that can be used in forbidden beasts, magic, or artifacts... or even for your own creations.
The goal is that elements shouldn't require the magic system and should have a clear established logic unique to them. I'll try to separate mundane, fantastic, and magical sources of damage. Before we continue magical simply means conceptually it is less defined by physics but more metaphysics, this isn't to say that mundane and fantastic sources cannot be magical or are magical, it is only a name.
Though while saying this ONLY Mundane should be Mundane. The only way to encounter anything but mundane damage should require exceptional circumstances. Hellfire should appear in hell for example.
Likewise I want to minimize the number of elemental damages that are handled better with the disease system or weapon system. It is why I didn't include Rust or barbs. In fact "Death" damage I also thought of, but honestly seems more like a condition. Nor do I want something that is better handled by magic. Though forgive me as I will include it anyway as is the nature of things..
Mundane
-Sonic: Simply speaking sonic does blunt damage, however unlike blunt it works on the entirety of the part and as such potentially does less or more damage. Being hit with a wall of sonic damage hits your entire body. As a special addition: Getting hit in the head with sonic damage, and it not being negated by armor, should cause temporary deafness (or permanent if we are being cruel)
-Light: Intense light rays deal heat damage but have a no-low chance of ignition. It also can be blocked by steam and smoke.
-Electric: Causes unrestricted heat damage randomly going through the body, as well it causes temporary muscular or sometimes neural failure in the body. The higher the electrical damage the more it fragments within the body causing more internal damage.
-Acid: Causes heat damage but also deals a minimum amount of damage regardless of the inflammability of the object, it also destroys itself and can be diminished by the stop drop and roll. Combusts when in contact with water or fire.
-But what of explosion?: Explosion is a combination of heat, sonic, and shrapnel
Fantastic
-Hellfire: This form of fire burns for a very long time and ignores the flammability of the object it is on, but cannot spread. Hellfire leaves no traces. It can survive water but it doesn't last too long after being doused.
-Frostfire: another form of fire but causes cold damage instead of heat, objects "destroyed" by it turn to ice/snow instead of slag/ash. It still follows flammability rules.
-Shatter: Causes piercing and slashing damage throughout the body in a similar method as electricity even fragmenting as the damage increases inside the body. Unlike electricity it is defended against by armor just the same.
-Dissolve: Causes general damage to whatever is touched. It just ceases to exist when destroyed, turning into dust.
Magical
-Sacred Fire: Acts like fire but is cancelable and doesn't cause harm in non-lethal combat. It burns bright but burns out quickly.
-Wither: Causes things to start to break apart, their strength serving as resistance, and living beings suffer intense necrosis as their flesh rots off. It has low penetration against non-living things like armor, but will ignore living beings.
--Alternative: Wither could cause the same rotting damage to inanimate objects but give random diseases to living beings.
-Psychic: Mitigated with Willpower this damage causes stunning and very low damage to the nervous system.