Thief's Aperture

You create two portals anywhere within range, which must be within 20 feet of each other. You can choose to not create the second portal, leaving the first one established but inert. The appearances of each portal is decided by the player, but they must be inverses of each other's color palettes.

The portals can fit a creature of Medium size or smaller through them, not allowing anything larger to cross, but a larger creature can move limbs through them as long as those limbs do not exceed the size of a Medium creature. The portals can be oriented in any direction, and an object or creature moving through one will retain the velocity they had when exiting the other. They last 10 minutes or until dismissed.

As a bonus action while they are active, you can choose to move one of the portals, or spend an action to move both, but they must remain within 20 feet of each other, and 120 feet from you.

You can place or move the portals through walls, but only if you are aware that there is an empty space past the wall.

They cannot be opened or moved within a creature or object, but can be opened or moved onto the surface BELOW that creature or object.

If you choose to dismiss the portals while a creature or object is partially through the portals, the portals will attempt to sever the two parts.

If it is an object, you must make a intelligence check with a dc equal to your own Spell DC. On a success, the object is pushed through in whatever direction you choose, with no damage. On a failure, the object is split in two pieces, one half ejected on both sides of the dismissed portal.

If it is a creature, it must make a dexterity save against your Spell DC + your own dex modifier. On success, the creature is pushed through in whatever direction it chooses. On a failure, the creature takes 4d4 slashing damage, and it is pushed backwards. If there is only a limb through the portals, on success it is pulled away, and on a failure the creature takes only 2d4 slashing damage, but the limb is severed.

Limbs are not severed if the creature resists or is immune to slashing damage.

At higher levels, the range between the two portals is increased by 10 feet and the damage is increased by 1d4 for every level spell slot past first level.