If I have a fire pierce jewel, does that pierce a fire shield or if I use a fire spell it pierces any shield or resist?
Great question! Pierce can be combined to "ignore" part of resist AND shields! Pierce will remove the % on the shields, and if you have more pierce than the shield, you will continue to pierce through the persons resist.
For example: 50 shield / 50 resist: You have 60% pierce. the shield will cancel out, and will therefore have 10% remaining which will further remove some resist. Therefore you will end up with 40% resist, instead of the 50% and 50% resist.
50 resist: You CAN remove all resist! You have 70% pierce, meaning you will pierce through ALL of the resist!
50 shield / 50 resist: You have 60% pierce. the shield will cancel out, and will therefore have 10% remaining which will further remove some resist. Therefore you will end up with 40% resist, instead of the 50% and 50% resist. 
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