Thief core class

Prime ability: Dexterity & Charisma; the Thief is as skilled with her tongue as she is with the blade. Anyone can move quietly, but Thieves can move silently. Anyone can hide in darkness, but Thieves can hide in shadows. Anyone can climb rough surfaces, but Thieves can climb sheer surfaces.

A party with a thief has a trap-finder/disarmer, someone who can scout ahead silently, and someone with a chance of being able to use arcane and clerical scrolls when there isn't a magic-user or cleric around.

Party Boon at Thief 1: But most importantly is the core Thief ability to Circle During combat: the thief takes advantage of distractions his allies provide in order to circle around behind a foe and attack. This isn't a backstab. It doesn't matter if the foe knows the Thief is Circling. The thief gets a +2 to-hit bonus from behind the foe, and upon a successful hit inflicts double damage.

If for some reason the target is unwary or unsuspecting, this becomes a Backstab: the to-hit bonus rises to +4 and triple damage is inflicted.

Personal Boon at Thief 3: At third level the core Thief gains Improved Evasion whenever awake, standing, and unhindered in any way. Traps and spell effects against which the thief successfully saves deal no damage. But even on a failed save, the thief only suffers half damage. Due to occupational exposure, the thief who reaches level 3 of the core Thief class also enjoys a +2 habituation bonus to saves against poisons.

When may the thief Circle? When an ally has dealt damage to the thief's target earlier in the round. Always double (Circle) or triple (Backstab) base die/dice damage first, before adding damage modifiers for Dex, item bonuses, etc.

A thief's Circle damage applies to any target, even non-humanoids (think dragons) or non-living humanoids (undead/golems). Thieves do not get triple damage against such foes, however.

Sneak/ambush damage for triple the rolled value can only happen if the thief is unencumbered and wearing light or no armor. Circle damage, however, is possible while lightly encumbered and even if the Thief is wearing medium (though not heavy) armor. Backstab requires total surprise. The foe cannot know/suspect that an enemy is able to attack from behind. Only living creatures are susceptible to backstab triple damage. Others may only be susceptible to double damage from Circling.

In group combat situations, it may be possible for thief to make an initial backstab, but in all likelihood he will only be able to Circle for the remainder of the combat. Given the requirement for Circling, a thief cannot Circle when he is alone without allies.