Advanced combat rules
 
AC vs Evasion
 
AC in basic combat rules is basically evasion + armor bonus. Let's separate it and introduce more advanced approach in two different ways.
 
Former touch AC = evasion (Ev)
AC = Armor class, represented by three numbers (Piercing, Bludgeoning, Slashing)
Example: leather armor (1/0/2).
 
AC is stackable. NAC (natural AC if it has some kind of natural armor like serpent scales) + armor AC.
 
Rolls for attack proceed as good old touch attack
 
Crystal has Ev 9 and is fighting against foe with longsword and MAB 2.
Foe rolls 1d20+2 against 9. Outcome is 17+2 = 19, attack wasn't avoided.
 
Foe rolls for damage and if his damage overcomes AC of damage type, damage passes through unchanged.
 
Foe rolled 7. which is greater than 2 from slashing AC, Crystal is hurt for 7 HP
If he rolled 1 or 2, damage would be absorbed by armor.
 
(possible modification: Damage comes all through if roll is bigger than AC*2. Lower roll halves damage, roll lower than AC is absorbed completely)