While you are holding this lantern, you can use it as a spellcasting focus for your spells, and you gain a +1 bonus to spell attack rolls and to the saving throw DCs of your spells.

Shock

When you attune to the will-o'-wisp lantern you learn shocking grasp cantrip and can use it untill you break an attunement. 

Variable Illumination. 

The will-o'-wisp lantern sheds bright light in a 5 to 20-foot radius and dim light for an additional number of ft. equal to the chosen radius. The you can alter the radius as a bonus action.

Invisibility. 

The will-o'-wisp lantern allows you to cast invisibility spell as an action. Once the spell has been cast two times, the lantern can no longer cast it until next dawn.

Consume Life. 

When creature drops to 0 hp within 5ft of lantern it must must succeed on a DC 13 Constitution saving throw against this magic or die.