Mob IRS

Mobs may be immune, resistant, and/or susceptible (IRS) to physical attack types (e.g. fire or blunt) and certain spells, just as PCs are.

However, they may also be immune, resistant, or susceptible to weapons with specified HITROLL bonuses. (NOTE: A weapon's DAMROLL bonus has no effect on a mob's weapon IRS modifiers).

The "KNOW MONSTER" spell can identify a mob's weapon IRS modifiers.

If a weapon bonus modifier is listed, then all weapons with that bonus level AND LOWER (or higher in the case of susceptibility) are included.

For example, if a mob is shown to be resistant to +4 weapons, then it is also resistant to all weapons with bonus values of +3 and lower. You can read this as "This mob is resistant to all weapons with a HITROLL bonus up to and including +4."

Similarly, if a mob is susceptible to +1, it is susceptible to all weapons with a HITROLL bonus of +1 or higher.

Note that if multiple weapon bonus values are listed, only the most extreme value is used. For Immunity & Resistance, the highest value is used. For Susceptibility, the lowest value is used.

So, a mob shown to be resistant to +3 and +4 is actually resistant to +4 weapons and below. The +3 modifier is redundant and can be ignored.

If a mob is immune to a weapon bonus, it is immune. Period. So if a mob is immune to +4, then it is immune to all weapons with a HITROLL bonus of +4 or less, regadless if it's also shown to be resistant or susceptible to such weapons.

However, if a mob is shown to be both resistant and susceptible to given weapon bonuses, the resistance and susceptibility modifiers will cancel if the respective bonus ranges overlap.

For example, if a mob is shown to be resistant to +4 and susceptible to +1, then the mob is resistant to weapons with a bonus of 0 or lower and susceptible to weapons with a bonus of +5. But for weapons with a bonus between and including +1 to +4, the resistance and susceptibility modifiers cancel out.

See also: IRS, RESISTANCES, SPELL KNOW MONSTER