Curious to see what you think about this homebrew rogue subclass...this is the second version of an Illusionist rogue I’ve been working on. One I’ve been wanting to play for a while. Appreciate feedback. Be harsh if necessary, I’m yet to learn how to balance these things :)

The Illusionist masters the arts of deception and disguise to confuse their enemies. Silver-tongued dramatists of the art of smoke and mirrors, an Illusionist cares only for the delight of trickery and victory through cunning, not muscles. Following this path is one of knowing that the Illusionist is the spider in the web, controlling everything from a distant place. By staying just one step ahead of their prey, the Illusionist will beguile and confuse before eventually dealing the unexpected killing blow.

Deceptive

When you choose this subclass at 3rd level, you gain proficiency with the Deception skill. You double your proficiency bonus when making any Deception check. In addition, you gain proficiency with the Disguise Kit.

Mislead

At 3rd level, you learn how to trick and confuse your enemies. You learn either Minor Illusion or Thaumaturgy. When you make an attack roll, you can force the target to make a Wisdom saving throw. On a failed save, your illusions mislead the target into thinking the attack is from another source. You gain advantage on the attack roll. On a successful save, they are immune to this effect for 24 hours.

Illusionist Spell Attack: Your proficiency bonus + your Charisma modifier

Illusionist Save DC: 8 + your proficiency bonus + your Charisma modifier

Smoke and Mirrors

At 6th level, you gain the ability to cast Fog Cloud and Mirror Image a number of times per day equal to your Charisma modifier. When you cast either of those spells, you can choose to immediately cast the other as a bonus action.

When you cast Fog Cloud, you can choose up to three creatures you can see (including yourself). Those creatures do not suffer the effects of the Fog Cloud.

Deadly Illusion

Your illusions gain an edge of real substance at 9th level. Whenever you have Mirror Image active, you can use a bonus action to choose an illusory duplicate and move it a number of feet equal to your walking speed (you retain all the effects of the spell, even in this fashion). You can also use your bonus action to make a duplicate make an illusory attack against a creature within 5 feet of it, using your spell attack bonus. The damage is 1d8 + your Charisma modifier psychic damage.

Due to the illusory nature of the duplicates, this damage cannot be increased or decreased by any means. It cannot benefit from advantage or disadvantage, and does not receive benefits from other players (like a paladin’s aura, for example). Duplicates cannot benefit from any items. The duplicates do not count as allies for the purpose of your Sneak Attack.

Master Illusionist

At level 17, your Smoke and Mirrors feature allows you to choose up to five other creatures. Additionally, when you use Mirror Image, you can switch places with any illusionary image of yourself as an action, and your duplicate’s damage increases to 2d8 + your Charisma modifier.

Sorry if this comes across the wrong way, but what makes this subclass stand apart from the Arcane Trickster? Reason being, at first glance I see a bunch of features that a trickster can also do. With that said, I see you're trying to put more emphasis on the illusions and mirror images. I would recommend taking a look what the Echo Knight (fighter), the Arcane Trickster (rogue), and the School of Illusion (wizard) and see how WotC made those subclasses.

I just looked at the Arcane Trickster and see what you mean. Not only is the Illusionist underwhelming compared to it, the abilities seem far less interestingly diverse. I think that moving away from the spellcasting aspect of the subclass and concentrating on new, different abilities unique to an Illusionist would solve the problem. Of course, that’s what I was trying to do in the first place...

I will revise this and share the next version with hopefully better features. But I was looking thematically for a subclass that would reflect the traditional art of real-life magicians and illusionists, with of course a D&D reimagination of them. I’m not trying to make a ‘School of Illusion’ rogue.