Okay, so, I think a good place to balance everything is:
lvl 3: +5 speed and str score for jumping in dim light or darkness, proficiency performance, 2/SR Shadow Dance
Shadow Dance: Advantage on Acrobatics and Athletics, and while in Dim Light or Darkness you can Dodge as a bonus action, hide while only lightly obscured, and use SA on a target if both you and the target are in dim light or darkness when you make the attack, even if you don't have advantage or an ally within 5 ft of the target.
lvl 9: You can teleport your speed as a bonus action while in Shadow Dance. Your speed increase while in dim light or darkness increases to 10ft. Alternatively: Your Speed increase while in dim light or darkness increases to 10ft, and you can use a bonus action to leap from or to a place of shadow with incredible ease, gaining a 10 foot bonus to high or long jump distance.
*the alternate ability could even be a little stronger, perhaps, but the idea is to give an ability that is different from the monk's teleporting. Instead of teleportation, you gain an incredible speed and leaping ability while in dim light or darkness, or while your landing area is in dim light or darkness. A third option might be a reaction teleport, but that again would compete with Uncanny Dodge.
lvl 13: You can summon weapons and tools of shadow. You can manifest any weapon or tool with which you are proficient out of pure shadowstuff as a bonus action. You can have as many shadow objects summoned as your Dex mod (maybe int mod, but only if we make int matter earlier in the subclass as well) at a time. Weapons summoned this way gain the light, finesse, and thrown properties, unless they are ranged missile weapons like bows or crossbows, and are magical. Shadow Objects disappear if they are not on your person for longer than 1 minute. Otherwise, they have all the same properties and characteristics of a normal object of that type.
*like most rogue subclasses, either 9 or 13 isn't a super powerful level. Instead, it's got a fun benefit that gives the rogue some unique tools.
lvl 17: I still like the shadow double, and I think that a full double that can attack once, gets no reactions, but does deal your SA, and has half your HP, would be really fun. Maybe it can use a reaction to take damage instead of you? Probably stronger than the Thief's 1 extra turn in the first round of combat, though. So, ditch it getting your SA damage.
If that is still too strong, I like going insubstantial while in Shadow Dance, getting extra damage with shadow weapons, or even greater movement benefits. Ignore all difficult terrain and Hide even while in plain view while in Shadow Dance?
Or get weird. While in Shadow Dance, whenever you reduce damage by half from either your Uncanny Dodge or Evasion feature, you gain extra damage with your Sneak Attack feature until the end of your next turn. When you deal damage with Sneak Attack, you roll d8s instead of d6s, and add your proficiency mod to damage.
What do we think about those options? It misses the idea of making an enemy attack target someone else, but since 17 is hard to pin down, we could put that in there? Perhaps when an attack misses, you simply make them reroll the attack against another target with reach?
I think I like the Sneak Attack boost at level 17, though, if we can't pin down a shadow double. It encourages you to put yourself in harm's way, but lets you punish enemies for attacking you. With a feat to get booming blade, you can also punish them for even moving, creating all manner of opportunity for lose/lose traps for your enemies.