Which items modify resistances/effects of monster from Isle of Ada?

Question

On the Isle of Ada there are couple of items which can modify resistances or effects of monsters - what is the list of those items and what exactly they do?

Answer 1

There are 2 items that can be used for purpose of enhancing your performance on Ada island:

1) Battle Tactics: You can drop it from Overseer Osverger (not guaranteed, though). After you use it once, it'll expire and, during the next 4 hours, you'll receive less damage from Raubritter Chastener, Skirmisher and Marksman.

2) Bottle of Enhanced Raubritter Lager: You can obtain it by using Meal from the Beak of a Night Harpy on a Bottle of Raubritter Lager. The Meal can be obtained by using a Nith Harpy Beak in a Millstone and the Bottle can be obtained as a drop from Raubritter Chastener. After consumed, during the next 4 hours you'll receive less damage from Night Harpies