Invoke Duplicity from the 2014 D&D rulebooks is not great, and Larian replaced it with a homebrewed version which is situationally better but much less interesting.

Playtest 6 of the 2024 Core Rulebooks for D&D overhauled the Trickery domain for Clerics, including making big improvements to Invoke Duplicity. This mod replaces BG3's homebrew Invoke Duplicity with a faithful representation of the playtest version, taking some inspiration from Echo Knight to fill the gaps in the description.

Recommended to be used with UA8 Healing Buffs for more viable healing on non-Life Clerics, especially when casting Cure Wounds at range via the duplicate.

Invoke Duplicity

You can use your Channel Divinity to create an illusory duplicate of yourself.

As a Bonus Action, you can expend one use of your Channel Divinity to teleport up to 30 feet to an unoccupied space you can see, and you create a perfect visual illusion* of yourself in the space you left. The illusion lasts for 1 minute, but it ends early if you have the Incapacitated condition or dismiss it as a Bonus Action.*

While the illusion persists, you gain the following benefits:

Cast Spells. You can cast spells as though you were in the illusion’s space*, but you must use your own senses.

Distract. When both you and your illusion are within 5 feet of a creature that can see the illusion, you have Advantage on attack rolls against that creature, given how distracting the illusion is to the target.

Move. As a Bonus Action, you can move the illusion* up to 30 feet to an unoccupied space you can see that is within 120 feet of yourself, and you can then teleport, swapping places with the illusion.

* Nature of the illusion
As a visual illusion, it does not affect creatures that are blinded or have Blindsight or Truesight. Attacks against such creatures will not gain advantage from the Distract feature, and they will themselves not attack the illusion or be less likely to attack the Cleric.

Illusions are tricky in D&D as there are hardly any rules describing how they work, leaving them up to DM interpretation. Since there's no listed way for enemies to destroy or disbelieve this illusion, my main concern was making sure it can't be used as an invulnerable tank... but that turned out not to be an issue as the AI is extremely reluctant to attack it and almost had to be forced to do so.

Defenses: Since the illusion isn't real, it can't be hit by attacks. Mechanically it has a very high AC and is immune to critical hits, meaning it almost literally can't be hit. It is invulnerable to any damage that gets through anyway, and is immune to all conditions.

It is recommended to use the Object Character Support mod, which will classify the illusion as an object instead of a creature in the D&D rules. This makes the illusion untargetable by most saving throw spells, largely preventing AI casters wasting limited-use spells on it.

Misdirection: At the start of their turns, enemies that are affected by the illusion (not blind/Blindsight/Truesight) randomly decide whether they think the Cleric or the duplicate is the fake, and are blocked from attacking it. They are more likely to think a closer target is real, and more likely to think the illusion is fake the more attacks have already missed it or otherwise been evaded. The miss counter is cleared if you swap places with the illusion.

While Spirit Guardians is active, nobody will believe the duplicate is real.
While Mirror Image is active, the target selection happens between the Cleric, the duplicate, and the remaining mirror images. I recommend using my 5e Mirror Image mod for this to make mechanical sense.

Despite my fears that the illusion would be an overpowered tank, when left alone the AI prefers to ignore the illusion and run for the Cleric. The misdirection logic creates a chance for the illusion to be targeted, but the AI will still generally prefer other targets when blocked from the Cleric.

* Dismiss
Dismissing is a free action on the duplicate, rather than a bonus action for the Cleric. Mostly to avoid cluttering the Cleric's bar, but it also matches how many similar features are implemented in BG3.

* Casting from the illusion's space
You get two different ways of casting from the duplicate's space, with different tradeoffs.

Control Duplicate: Activating will instantly swap places (and near-instantly swap VFX) with the duplicate, to give the illusion of controlling the duplicate to cast a spell. This is the best representation of the feature as you actually are in the duplicate's space casting the spell.

You're invulnerable and immune to surfaces and some persistent spell effects while swapped, to avoid effects the duplicate wouldn't be affected by, but this is not a perfect match for the duplicate's protections, so swapping into dangerous situations carries some risk.
The granted immunities can also end currently applied effects, which is not intended, so to prevent exploits you are not allowed to use this feature while afflicted with certain conditions.

Cast Near Duplicate: Alternatively, you can remain in control of the Cleric but enable casting spells at targets around the duplicate. There is both a passive toggle and a free action to do this. While enabled, your melee spells will be able to hit targets near the duplicate from any distance.

The action enables casting from range temporarily and disables melee actions that aren't allowed from the duplicate's space, to make it less confusing which actions work from range and which would make the Cleric run to the target. The toggle passive does not disable unsupported actions as it's made to potentially be left on permanently.

You can still cast melee spells at targets around the Cleric while this feature is enabled, but you won't automatically move to the target if even slightly out of range, which can be annoying. Clicking on the ground to move works.

Any push/pull effects will be based on the Cleric's position rather than the duplicate's, which is not correct.

* Moving the illusion
In D&D, the duplicate doesn't have its own initiative and is only moved on the Cleric's turn. The Cleric is given a "Move Duplicate" bonus action to do this, but proper previewing of movement in BG3 is only supported for a character moving on its own turn, so the duplicate is also given a turn and ability to move, though its movement must first be unlocked by using the bonus action and is only available if the Cleric and duplicate were lucky enough to get shared initiative.

The Move Duplicate action can be used multiple times, and only the first use will cost a bonus action. Once used, the duplicate's remaining movement is displayed as the duration of the "Duplicate Movement" buff applied to the Cleric.

If the Cleric tries to order the duplicate to move further than it can reach, you get a ping at a location the duplicate can reach in the same direction.


Extras

Toggle Helmet
The duplicate has a free action to toggle its helmet. The setting is remembered for new duplicates from the same Cleric.




Compatibility

Can be used together with other mods that modify the Trickery domain or Invoke Duplicity itself, but will completely replace Invoke Duplicity and be unaffected by any changes other mods make to it (specifically compatible with Cleric Subclasses, and tested with Trickery Domain Overhaul.)
This mod should be placed after (below) other mods affecting Invoke Duplicity in the load order.

Object Character Support should be placed before (above) this mod in the load order, if used.

Invoke Duplicity Equip Fix is built-in and not required.

The Spirit Guardians aura is modified to support suspending it while controlling the duplicate. This change is shared with and compatible with my Echo Knight mod. Load order between the two mods doesn't matter.

This mod patches the target conditions of hundreds of spells, including ones added by mods. This makes spells from other mods support use from the duplicate's space without them having to even be aware of this mod.

Patching is done dynamically on startup via Script Extender and shouldn't cause any conflicts with other mods as long as they're properly written. I can't guarantee this won't break things if a spell has syntax errors. Unfortunately BG3 is quite lenient in accepting garbage input, and not all mods are properly written.


Known Issues

High Ground bonuses apply when the Cleric makes melee attacks from a distance using the duplicate.

Ordering the duplicate to move will sometimes cost less movement than it should, only representing a straight-line distance rather than the path actually taken. The game is inconsistent in if the movement cost is deducted or not when the move is ordered. When it's not, I use the minimal possible distance.

The duplicate will not work correctly if you change the Cleric's body type using Appearance Edit Enhanced.

Game issue: Every time you summon a temporary character - duplicate or otherwise - it leaves behind a lot of database entries in the save game, which gradually increases load times. The Database Cleaner mod can be used to clean up most of the remains.


Credits

Huge thanks to Norbyte! This mod would not be possible at all without Script Extender.