Elder Tanuki Card card_starlit_stairs

What it is for

Card: fits into Right hand gear that has a free slot.

Chance to cast a Ghost strike on attack 9%. Damage against bosses +35%.

Weighs 2 of your carry capacity — and weight is what stops drops once the bag fills up.

The best source is Elder Tanuki, at 0.020% per kill. You can farm it at Starlit Stairs.