O, naturally, I make the mistake, it's of course the "Talisman of the North".
Yes, I'm very sure it is this Talisman I become in the Tunnels by using the 3 other Talismans (West, East, South) ! I'm sure because I used this Talisman just for the Hide in Shadows Skill in the battle against Amdusias !
Maybe, but I don't know (maybe someone of the devs of Larian can affrim this?), it is because I start a whole new game AFTER the patch ? ( patch : including the nightmare mode & more things I believe! I'm playing the European Xbox version, but I suppose this is the exact SAME one as the one coming out the 12th of april in America ?) .
But also to say I go for that Talisman of the North when my hero was already L 13 or L 14 ! Maybe the Talisman is also in some way "based on the hero's current level" like many chests are level based (+ have their own level) Macbeth of the Larian Team write down earlier somewhere on this forum .
Edit: I will also check the Level of my Talisman
(edited after reading Lancet's edit

)
I'm not totally sure about the other boosts on the Talisman, I will check this and let you know Lancet.
Later on I will check also your Guide (but I'm only L 19 and does not wish to read possible "spoilers") to see or I met other kind of boosts on gear ...