Friendship is a new stat introduced in Tiny Tina's Assault on Dragon Keep DLC
Its exact effect is not confirmed, altough various speculation has been going around. One of them is that the Friendship factor affects the magnitude of buffs you receive from your "Frenemy" allies such as the Pixies. Another speculation was that the amulet enhances various stats such as Damage, Max Health, Health Regen, Shield Regen, etc. However, this is proven to be incorrect.
The only effect that is confirmed and recreatable is that, when worn in a party of 2-4 people in Coop, it will generate a pink cloud at the players' feet if they have the amulet equipped. With two people, pink and red heart particles appear, and yellow star-shaped particles will appear as soon as three or more people have it equipped. The cloud seems to be slowly growing in size and visual appearance over time, untill it nearly fully covers the players' legs.
