Sneak Attack: Beginning at 2nd level, you deal extra damage when you are flanking an opponent or at any time when the target would be denied its Dexterity bonus to AC. This extra damage applies to ranged attacks only if the target is within 30 feet. See the rogue class feature, page 50 of the Player's Handbook. This damage increases at 4th, 6th, 8th, and 10th level.

Envenom Blade (Ex): At 5th level, your saliva becomes venomous. As a free action three times per day, you can envenom your melee weapon, a thrown weapon, or a piece of ammunition for a ranged weapon. Using this ability does not provoke attacks of opportunity. The Fortitude save DC of the venom is equal to 15 + your Wis modifier. The venom deals 1d4 points of Constitution damage as its primary and secondary damage. If you already have a bite attack, you can choose to envenom your bite as a use of this ability.

Immunity to Scorpion Venom (Ex): At 5th level, you gain immunity to all scorpion poisons (but not to the poison of other creatures).

Scorpion's Sense: At 7th level, you gain Scorpion's Sense (see page 53) as a bonus feat.

Tail of the Scorpion (Su): At 9th level, you learn to grow a dark, translucent scorpion's tail once per day, which magically emerges from whatever clothing or armor you're wearing. The stinger on the end of the tail deals the damage indicated on the table below, + 1/2 your Strength bonus (if any). The DC for the poison save is 10 + 1/2 your Hit Dice + your Con modifier.

You can wield a weapon in one or both hands at your normal attack bonus and make a secondary natural attack with the tail at a —5 penalty.