Weaknesses and Resistances

In most RPGs there are damage types that respond differently to each other. In Pokemon Fire types beats Grass, Grass beats Water, and Water beats Fire. In Fire Emblem Lances beats Sword, Swords beats Axe, and Axe beats Lance. These systems can range in complication to varying degrees but it all comes down to weaknesses and resistances.

Weakness If a character has a weakness to a damage type they have disadvantage on defense rolls against that damage type.

Resistance If a character has resistance to a damage type they have advantage on defense rolls against that damage type.

This system could be easily implemented in D12. You could literally yank whatever weakness or resistance system best fits your story, but you could always create your own.

First, list the specific elements you want to use (Example: Air, Earth, Fire, Water). Then put them in order of who has resistance over who (Example: Fire > Earth > Air > Water > Fire). Then give the monsters an elemental trait and natural attacks (Examples: Fire Breath, Toxic Earth Claw, Water Saw).

Then when the players use an attack have them classify it with an element if applicable, compare it with the creature’s trait and see if the monster has a weakness or resistance against the attack, and then roll defensive rolls appropriately.