Surely if he took both your damage from the backstab it wouldn't have shown just the damage you inflicted, if he died in 1/2 backstabs at the same time it would have just shown 1170. As for the edited humanity ive never seen that before but I do know the is 2 types on the editing program so maybe him selected the wrong type.
The engraved gauntlets give a chance for a normal hit to do the damage of a critical hit, like a backstab or riposte. Keep attacking until you trigger a critical hit from the gauntlets, then take off the gauntlets. Every hit will now become a critical, for a lot of damage.
Start: Opens the game menu – this does not pause the game (there is no pause in this game). Things can still attack you, and you can still move with the left analog stick, but the buttons control the menu operations (your shield is down, you cannot sprint, attack, etc). While using the menu you can hit Start again at any time to immediately

Greatsword +15. Greatsword is a Weapon in Dark Souls and Dark Souls Remastered. One of the gigantic straight greatswords. Very few have what it takes to wield this incredibly heavy, damage-dealing monster." "A favorite of the Knights Berenike, known for their heavy armor, and Black iron Tarkus."

884 hours registered with KBM. Rank 2 in Brotherhood of Blood. It's entirely possible; in fact, I believe that aiming my beloved Crypt Blacksword's attacks with a controller would be imposible. You two may try to use autohotkey and find a Dark Souls 2 config.
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how to backstab in dark souls 2