Gatekeeper

A typical individual sees a door and doesn't question what lies on the other side, but when a gatekeeper is known to be in the area, caution should be taken. What was once a mundane passway or gate leading just into the next room might instead open up into a mind-bending maze or a pit full of deadly acid, and the layout of a building might seem to be entirely different from how it appears on the outside if a gatekeeper lives within.

Gatekeepers channel their magic into doors or gates, which they can place virtually anywhere but are limited in duration. They do this by making their doors pass through the Ethereal Plane, while making transport through this realm imperceptible to any who pass through. Particularly skilled gatekeepers can conjure doors that lead to an entire demiplane of their own design; this ability can serve many purposes, whether the gatekeeper needs a trap to defend an area or a safe location to take a brief respite.

See Destination

Beginning when you select this subclass at 2nd level, when you touch a door, you can use an action to cause it to become partially translucent, allowing you to see anything within 30 feet of it on the other side. You also learn whether the door is enchanted in any way, and you learn about any glyphs of warding on it.

Traverse Ether

Beginning at 2nd level, you've learned to create your own doors which can pass a short distance through the Ethereal Plane. As an action, you can create a Medium door on a surface you can see within 30 of you. The door can be standing alone, or it can be integrated into a wall or other vertical surface, and you choose the appearance of the door. Simultaneously, another identical door appears at a location of your choosing that you can see within 60 feet of the original door. Anything that passes through one door is instantly transported to the other, including the effects of spells and projectiles.

You can decide whether either door is initially locked, and a creature that attempts to unlock it must make a Dexterity (Sleight of Hand) check versus your spell save DC, unlocking the door until the start of your next turn on a success. Additionally, a creature can make an Intelligence (Investigation) check versus your spell save DC to determine that the door is magical in nature. Both doors disappear at the end of your turn, three rounds after you place them, and any surfaces the doors were part of are restored to their original form. You can use this feature a number of times equal to your Intelligence modifier (minimum of 1) per short rest.

Redirect

You've learned to extend your magical abilities from your own doors to doors that already exist, forming a more powerful connection. You can touch a mundane, nonmagical door, and it becomes linked to you for the next minute. During that minute, you may choose a location within 400 feet of the door that you can see. An identical door appears there, and the original door becomes magical and now leads to the destination door rather than the area previously on the other side. Anything that enters it is immediately transported to the destination door.

After an hour, the destination door disappears, and the original door returns to being mundane. Until then, if the room connected to the door has no other entrances, it is inaccessible by mundane, physical means. This effect ends early if dispel magic is cast on the original door or on the destination door.

Improved Traversal

Your magic becomes more potent, enabling your doorways to form even stronger connections. When you use your Traverse Ether ability, the destination door can now be up to 300 feet from the original door, and the doors disappear after one minute rather than after 3 rounds.

Furthermore, you can choose to create doors that are invisible to anyone besides you. A creature that enters the space of such an invisible door, if unwilling, must make a Dexterity saving throw against your spell save DC in order to avoid being transported.

Final Destination

Your power has grown such that it transcends the bounds of the material plane, allowing your doors to access areas that do not exist within this reality. When you use your Traverse Ether or Redirect ability to create or alter a door, you can choose not to create a destination door and instead have the door lead to a small demiplane, choosing one of the following destinations. A creature that enters one of these doors must make a Dexterity saving throw against your spell save DC in order to avoid being transported, and they have disadvantage on this saving throw if the door is invisible.

• Acid/Lava Pit. This demiplane is a small stone room that is a 15-foot cube, at the bottom of which is a pool of acid or lava (your choice) 5 feet deep. A creature that enters this demiplane falls forward into the acid or lava as gravity readjusts, positioning the exit door at the top of the room instead of the side. A creature that touches or starts its turn in the acid takes 14 (3d6) acid or fire damage at the start of each of their turns.
• Web Chasm. This demiplane is a 5-foot wide, infinitely deep ravine between two stone walls, filled with thick, dense cobwebs. A creature that enters this demiplane or starts their turn within it is restrained by the webbing, and can use their action to make a Strength check against your spell save DC in order to break free from the cobwebs. If they fail, they fall 10 feet and are restrained again, but if they succeed, they can avoid falling and use the webs and walls to move up to 15 feet in any direction.
• Monster Arena. This demiplane is a floating stone platform in an infinite sky-blue void. On the platform is a creature of your choosing with a challenge rating up to your proficiency bonus. The creature can be an Aberration, Beast, or Monstrosity. This demiplane's exit door disappears as soon as a creature enters, but if the monster you chose is killed, the exit door appears on the platform and any other creatures within are free to leave.
• Labyrinth. This demiplane is a twisted, convoluted maze made of stone brick. The exit door vanishes when a creature enters the maze and then reappears at a random location within it. The creature must make an Intelligence check against your spell save DC in order to find the exit door. The exit door is visible regardless of whether you made the entrance door invisible.

When you create such a door, it stays in existence indefinitely, but if the door is opened or traveled through, it reverts to normal one minute later and the demiplane disappears. When the demiplane disappears, any creatures within are expelled into the nearest unoccupied space to the original door's location. You can only have two doors that lead to demiplanes at any given time, and if you create a third, the oldest one disappears and any creatures within it are expelled.