This scorpion is a normal giant scorpion with the Advanced simple template. It was constructed because several Paizo adventures (and at least one Pathfinder Society Scenario) references them.
AC 20, touch 11, flat-footed 18 (+2 Dex, +9 natural, –1 size)
Sting—injury; save Fort DC 17; frequency 1/round for 6 rounds; effect 1d2 Strength damage; cure 1 save. The save DC is Constitutuion-based and includes a +2 racial bonus.
Grab: If this creature hits with a claw attack, it deals 1d6+6 damage and attempts to start a grapple as a free action without provoking an attack of opportunity. It may only grab Medium or smaller opponents. The centipede has the option to conduct the grapple normally, or simply use its claw to hold the opponent. If it chooses to do the latter, it takes a –20 penalty on its CMB check to make and maintain the grapple, but does not gain the grappled condition itself. A successful hold does not deal any extra damage.