Get the Auspicious Tarstone for Increased Critical Chance Easy. From Widow's Overwatch beacon run to the right and take the path past the 3 guys and head to the left. You will get to Mushroom Village with some witches and an organ grinder. Easy to kill, you have to light 3 candles(Offerings) then head back to the start and open the chest. Will be the Auspicious Tar Stone. Make sure to look for the Mushrooms on the way and get the Beacon so it is unlocked.

0:00 Start
0:50 Mushroom Village
2:29 1st Offering
2:59 Mushroom Village Beacon
4:30 2nd Offering
5:40 3rd Offering
5:53 Chest
6:40 Auspicious Tarstone

Levels
Level 1: Improves melee Critical Chance.
Level 2: Melee attacks have +10% Critical Chance.
Level 3: Melee attacks have +15% Critical Chance.
Level 4: Melee attacks have +18% Critical Chance.