This is my first post here
first of all hello everyone :)

my question is about pendant of the elf +4.
it gives immunty:mind affecting spells.
before i got the pendant upgraded, at level 13 , i chose slippery mind for my second rogue only feat.
Is slippery mind allows you to reroll for will saves against mind affecting spells ? so then this feat is useless while i'm using the pendant +4 ? Or did i understand the abilities of the feat and amulet completeley wrong (i hope i did) ???
thanks for the answer...

If you get immunity from the pendant, then yes, any feat that does the same (but not as good) is useless to you.

Correct: Slippery Mind has no use when wearing an object that gives immunity to mind-affecting spells.
When you have good savingthrows, though, you might consider wearing an other amulet, that gives you better saves or immunity to some of your weaknesses.

Mmh, seems Tal finished his post when I just started...