Shield Master (Combat)
Your mastery of the shield allows you to fight with it without hindrance.
Prerequisites: Improved Shield Bash, Shield Proficiency, Shield Slam, Two-Weapon Fighting, base attack bonus +11.
Benefit: You do not suffer any penalties on attack rolls made with a shield while you are wielding another weapon. Add your shield’s enhancement bonus to attack and damage rolls made with the shield as if it were a weapon enhancement bonus.
Emphasis is mine.
So (provided you have the TWF feat):
1) do you have to apply TWF penalties (-2 for light shield) to attacks made with the weapon you are fighting with?
2) if you use a heavy shield, do you apply a -4 penalty to attack for those attacks for which you use the weapon?
Thanks
You take no penalties to attacks made with the shield.
The longsword(example) takes whatever penalties it would normally take however.
Though i doubt thats RAI bbt.
The devs always assumed the shield would be in the off-hand that is why shield bashing is written like it is in the equipment section.
I am tempted to run DPR numbers on it to see if I would ever allow it or not.