Tried testing out Rancor Mantle:
I took 1100 damage from 1000 needles with just rancor mantle on.

Just mantle:



I took 1100 damage from 1000 needles with rancor collar and mantle on.

Mantle and Collar:



This suggests the effects are not stacking.

MNK/SAM with RR, GH, DD on Abyssea Grauberg crabs got 698 crits in a row w/ rancor mantle on and no other crit gear. This means the mantle should be at least 5% crit rate.


MNK/SAM with RR, GH, Mounted Champ on Abyssea Grauberg crabs got 1509 crits, 363 non-crits w/ rancor collar and rancor mantle. That is 80.6% crit rate.

So, it appears that the effects of both the mantle and neck do not stack. I did not test for any other properties of the mantle if they exist.