This onyx feather seems to be made of pure darkness. While holding the feather, you are resistant to necrotic damage and have advantage on attack rolls against creatures who's alignment is the polar opposite of yours.

The feather has 10 charges. You can expend a number of charges to cast the following spells (save DC 17) from it: animate dead (3 charges), blight (4 charges), blindness/deafness (2 charges), disintegrate (6 charges), and power word: kill (9 charges).

If all 10 charges are expended, the feather turns to ash and is destroyed.

Notes: Resistance: Necrotic, creature of non-good alignment, Combat