Dimensionless Slash

You coat a blade in darkness. When making a melee attack with the coated blade, the darkness gives a +6 to hit, and does 5d8 necrotic. On a critical the blades darkness can be used to teleport the target to the Ethereal Plane, where they must spend at least one round. This uses up the darkness. The darkness also gives the blade three charges. These charges can be used several different ways;

1 charge:
Sends the user to the Ethereal Plane/Material Plane.
Let's the user see into the Ethereal Plane/Material Plane.
2 charges:
Allows the user to send a wave of necrotic damage in a line, up to 60 ft.
3 charges:
Allows the user to see and then attack someone/thing in the Ethereal Plane/Material Plane in one action.