Resonance Stone

Description

This is a very powerful item if used correctly. You can pair it with psychic damage sources like Shadow Blade, Shadow Strike, etc., to double the damage output.

It does come with a risk of inducing mental saving throw disadvantage - intelligence, wisdom, charisma. However, this also works well for your casters, which now get an easy way to apply most of the spells if starting early in the round.

Some tactics - have high dexterity (maybe even Alert​), get Counterspell,​ and you should be ready for most of the surprises that come your way during combat to circumvent the negative aspect of Resonance Stone.

Location - Resonance Stone

Located inside the Mind Flayer Colony, late into Act 2. This area will be reached as part of the main story progression.