If I use a sun spell Extraordinary with 15% pierce together with a star spell infallible 15% pierce, how does that work? Also if my opponent has a shield ward together with a body resistance, does my armor pierce pierce them all?
Yes, pierces stack. and you don't necessarily pierce all of their resist unless you have an insanely high amount. Lets say you have 70% pierce and pierce through a 50% tower, and the enemy has 65% base resist, after the 50% tower, you have 30% pierce left, making you pierce 30% of the 65% resist. So that leaves the enemy with 35% resist to resist your attack. Hope i helped!
If I use a sun spell Extraordinary with 15% pierce together with a star spell infallible 15% pierce, how does that work? Also if my opponent has a shield ward together with a body resistance, does my armor pierce pierce them all?
The enchantment and aura stack, so you can use both.
Yes, your pierce will work on their ward and resistance, but I believe the wards are pierced first (in other words, you have to fully pierce the entire ward before cutting through their resistance).