Portal Thief

I love the idea but it feels like its missing somesmall things. I never liked that you have to get to level 17 to max out a rogue subclass. Also a rogue basically needs skills nd tools. This subclass is amazing but it perfect other feats, as such you would be forgoing skill based feats so I added some in to level 3. Feel free to share your thoughts. 

This is what I came up with:

Rogue Subclass: Portal Thief

A Portal Thief is a rogue who has learned to manipulate folds in the Weave to tear open rifts in space, slipping through reality itself to infiltrate, escape, and strike from impossible angles. These elusive operatives are infamous for vanishing from locked vaults, bypassing arcane wards, and appearing behind their targets with a blade already drawn.

3rd Level – Dimensional Insight

Your exposure to spatial folds and arcane distortions has sharpened your perception of hidden patterns and unstable boundaries.

• You gain proficiency in Arcana.
• You also gain proficiency in one additional skill of your choice from the following:
  Investigation, Sleight of Hand, Stealth, or Insight
• You gain proficiency in any two tools of your choice.

3rd Level – Distortion Dash

You can tear open a rift in space and step through it in the blink of an eye.

• When you take the Dash action on your turn, all movement gained from the Dash occurs as teleportation instead of normal movement (walking, climbing, etc.).
• You must have line of sight to your destination, unless the location is previously known to you.
• This teleportation does not provoke opportunity attacks and occurs instantaneously.
• If you teleport to a space within 5 feet of a creature, your next melee weapon attack against that creature before the end of your turn qualifies for Sneak Attack, even if you don’t have advantage and no ally is adjacent, and do not have disadvantage.

Previously Known Location: A location is considered previously known if you have seen it within the past 24 hours, or studied it via magical means, maps, or surveillance.

6th Level – Cloak and Dagger

Your portals become more stable, allowing for reactive escapes and stealthy repositioning.

• After you deal Sneak Attack damage to a creature, you may immediately teleport to an unoccupied space within 15 feet or half your movement speed (whichever is greater). This teleportation follows all rules of Distortion Dash.
• After teleporting this way, you may choose to become invisible until the start of your next turn, or until you make an attack, cast a spell, or interact with an object.
• You may use this feature a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

10th Level – Gateway Portals

You can now create large, stable portals for infiltration, escape, or tactical redirection.

• As an action, you may create a pair of gateway portals in two locations within 120 feet of you. You must have line of sight to each location, unless they are previously known to you.
• Each portal is a 10-foot diameter sphere that occupies its space and lasts for 10 minutes or until dismissed as an action.
• You may only have one pair of active gateways at a time.
• Any creature may use a bonus action to teleport from one gateway to the other, arriving instantly in the paired portal’s space. When a hostile creature attempts to move through a gateway for the first time on a turn, it must make a Wisdom saving throw (DC = 8 + your proficiency bonus + your Intelligence modifier). On a failure, it is repealed back to its previous space and cannot pass through the portal that turn.

14th Level – Ambush

You become a blur of blades and portals, striking from every angle in a storm of spatial chaos.

• Once per long rest, you may activate this feature as part of the Attack Action:
• Choose a creature you can see or whose location is previously known to you within 60 feet. You teleport to an unoccupied space within 5 feet of it and make a melee weapon attack. This teleportation follows all rules of Distortion Dash
• You may then repeat this teleport-and-attack sequence a number of times equal to your Dexterity modifier (minimum 1). Each new target must be within 60 feet of the previous one and must be a creature you can see or whose location is previously known. You may target the same creature more than once, but not in direct sequence (i.e., you must target a different creature before returning to the same one).
• Each attack made after teleporting deals an additional 1d8 damage of the same type as the weapon used.
• During this feature, your attacks crit on a roll of 19–20.

Seems like the best subclass