Ethereal Strike

You select a target that you are familiar with (to be considered familiar, you must have seen the target, or have seen a detailed picture of the target and know its name or know its voice). The target must be within the Inner Planes at the time of casting for the spell to work. 

You step into the border regions of the Ethereal Plane, in the area where it overlaps with your current plane. You remain in the Border Ethereal for the duration or until you use your action to dismiss the spell.

During this time, you can move in the Ethereal plane as if it were your home plane. If you move up or down, every foot of movement costs an extra foot. You can see and hear the plane you originated from, but everything there looks gray, and you can't see anything more than 60 feet away.

While on the Ethereal Plane, you can only affect and be affected by other creatures on that plane. Creatures that aren't on the Ethereal Plane can't perceive you and can't interact with you, unless a special ability or magic has given them the ability to do so.

You ignore all objects and effects that aren't on the Ethereal Plane, allowing you to move through objects you perceive on the plane you originated from. During your time on the Ethereal Plane, you know the fastest way to reach the entity that you targeted, unless they are under a spell like Sequester. You can see your target on the Ethereal Plane, even if they have cast a spell like Invisibility on themselves, or are in magical darkness. 

When you get within striking range of your target, and take your attack action with the glass dagger, the target must make a Constitution Saving Throw against your Spellsave DC. If the target is unaware of your presence, they make this save with disadvantage. On a failure, the target takes 8d12+20 Force Damage, or half as much on a success. 

When the spell ends, you immediately return to the plane you originated from in the spot you currently occupy. If you occupy the same spot as a solid object or creature when this happens, you are immediately shunted to the nearest unoccupied space that you can occupy and take force damage equal to twice the number of feet you are moved.

This spell has no effect if you cast it while you are on the Ethereal Plane or a plane that doesn't border it, such as one of the Outer Planes.