I’m pretty sure it does not stack.
“Enemies have +50% damage” would stack because of the “+” but “Enemies have 40% Endurance” would not stack, it is a set value.
I think it’s the same for “Deadly”.
Thank you for the replies.
I thought as much, but wanted to make sure before charging in.
A couple of the rewards were quite juicy & I didn’t want to risk losing them.