What is the Impromptu archetype?
The Impromptu Archetype is Bluepoch’s first real foray into archetypal team building, with it being the first one to introduce a unique mechanic exclusive to the units that belong to this group.
In simple terms, this archetype revolves around the special incantation, called [Impromptu Incantation], which performs as the team’s damage dealer (instead of there being a unit that acts as the lead carry). When certain conditions are met, an [Impromptu Incantation] is generated at the tail end of the AP Area, which will then fire off attacks at the end of your team’s turn. In a way, all the units within the archetype act as supports for [Impromptu Incantation], interacting with and manipulating it; from having it apply debuffs on the enemy, giving it damage scaling, or increasing its attack instances.
[Impromptu Incantation] is a separate entity from your team (as can be seen in the score boards, where it appears as its own entry). It inherits average the team’s total stats, which means that unlike other teams, it’s important for Impromptu teams to have equal amounts of investment across their characters. To bring out this archetype’s full potential, it’s imperative to learn how to cycle through the team’s Ultimates, recognize opportune burst windows, and know proper AP allocation for the units in the team.
Normally, [Impromptu Incantation] does not have an Afflatus which means it cannot benefit from Afflatus DMG Bonus. Some characters can change it's Afflatus typing, 
Barcarola (Star), 
Paper Heron (Plant).
How to play Impromptu?
Understanding how Impromptu works can be daunting at first, but the gameplay loop can be simplified like so:
Whenever the team consumes [Eureka], stacks of [Inspiration] are generated.
On the following round, the total [Inspiration] is distributed randomly among all your cards, with the amount ranging from 1~5 per card (pre-merge), with some units having mechanics that break this upper limit.
Choosing cards with [Inspiration] on them adds to a tally, which will then transform into [Impromptu Incantation], which attacks at the end of the team’s turn.
The higher the amount of [Inspiration] tallied, the higher [Impromptu Incantation]’s damage multiplier and attack instances become.
Rinse and repeat.
Consuming Eureka is also not something that requires a lot of management since all Impromptu units automatically consume Eureka whenever they cast any of their Incantations. In a way, Impromptu teams play themselves to an extent, leading to a high damage floor with minimal effort. This makes the Impromptu team a relatively auto-friendly set-up. However, there's a lot of optimization that can be done within your rotation.
In Depth: Maximizing the team’s damage and maintaining a stable rotation for consistent, high amounts of damage is a completely different story however. While the game plan of Impromptu can be as simple as “click cards with big numbers = get machine gun / shotgun with big damage,” optimizing [Impromptu Incantation]’s damage can take a few extra steps and more mindful decision-making.
Let’s start with the biggest way to see a spike in your Impromptu team’s damage — recognizing burst windows using the team’s main support unit:
For the classic Star Impromptu, this is
Aleph, while for the Plant Impromptu, this is 
Tooth Fairy. Both of these units’ Ultimates exponentially increase your [Impromptu Incantation]’s damage on the turn they’re cast via [Hyperthymesia] and [Neuralgia], respectively.When these effects trigger, you want to accrue as much Inspiration stacks as possible during that round, and ideally, cast the Ultimates of your other Impromptu units alongside them to maximize these effects.
Maximizing Aleph’s Ultimate is also a bit trickier because it’s a 2-turn channel, and there’s the [Memorize] aspect that you also need to consider.
In most cases, you’d want to [Memorize] the cards that will provide big increases to [Impromptu Incantation]’s damage, such as
Barcarola's [Cascading Arpeggios] for increased attack instances or any of 
Matilda's cards for Critical DMG Bonus.
Next, let’s talk about ramping up and maintaining your Impromptu’s damage:
This all boils down to managing your Afflatus driver’s Ultimates:
Barcarola for Star and Paper Heron for Plant.Barcarola wants to maintain her [Quartet] on at least two other teammates at all times. This is what allows the team to gather and expend tons of Inspiration since Barcarola drains the [Eureka] of allies in the [Quartet] status whenever an Attack card is played. It’s possible to maintain it on all three allies to maximize [Impromptu Incantation]’s damage, but the rotation becomes tighter and can fall apart from bad RNG.
To help facilitate this, using the "Unfinished Tune" tuning is important, and using techniques like merging to maximize Moxie gain is necessary to learn when piloting a Star Impromptu team.
As for Paper Heron, piloting her team is much simpler and more forgiving. You’ll still want to run the “Unfinished Tune” tuning to force Paper Heron cards when needed. Paper Heron needs to maintain her [Qi Panorama] Array, which lasts for 4 rounds and can be refreshed or re-deployed with her Ultimate.
The game plan with Paper Heron is to simply maintain her [Reader of Qi] buff on the team and ensure that she can re-cast her Ultimate every 3 turns, ideally in tandem with Tooth Fairy’s Ultimate.
Another important thing to note is maintaining the crucial buffs for the team. For the Star Impromptu team, maintaining 4 stacks of Aleph’s [Clarification] during your burst window is ideal. Meanwhile, Paper Heron’s [Reader of Qi] is what should be maintained for Plant Impromptu.
Finally, you also want to maintain Tooth Fairy and Aleph’s [Continuous Action I] buffs. Remember, one more card cast means more Inspiration funneled into [Impromptu Incantation].
By following these concepts, you can maintain a stable and high damage performance from your Impromptu team. If it seems like a lot (which it can be), but at the bare minimum, you want to maintain [Quartet] and/or the [Qi Panorama] Array.
But what are the benefits to playing Impromptu over other Archetypes, and what may make you reconsider?
High frontloaded damage, capable of easily clearing stages with minimum effort.
Very high damage floor due to [Impromptu Incantation]. taking the team's average stats and scaling significantly with [Inspiration] funneling.
A very easy team to pick up and pilot for beginners, while having a nice learning curve to further optimize the team’s damage for the more try-hard players,
Very auto-friendly team for general content, and even for some harder content.
Unlike other teams, the archetype requires a modicum of investment, not just from owning the archetype’s units (and the units that give Impromptu an Afflatus like Barcarola or Paper Heron), but ensuring that each character is equally invested into because of how the Impromptu Incantation’s stats work.
Teambuilding is relatively inflexible (when it comes to BiS). On top of needing units that can expend Eureka, you ideally want to use other Impromptu units to maximize the Impromptu Incantation’s damage.
Members of this archetype (except Kiperina) cannot work as standalone units and the archetype’s support core cannot be used as “wheelchairs” for other units, unlike other archetypes that can borrow and lend their supports to and from other teams.
The classic Star Impromptu is currently falling behind in the meta when compared to its contemporaries, being the first real archetype introduced in the game, and hasn’t received any attention from the developers in almost over a year (bar the unexpected interaction between Paper Heron and Barcarola).
Teambuilding
There are two main teams that can be assembled from this ensemble of Impromptu units: the Star Impromptu team with Barcarola and the Plant Impromptu team with Paper Heron. While these two units are what gives [Impromptu Incantation] its Afflatus and DMG type, the other members are just as important in making the team stronger:
Plant BiS:
Paper Heron / 
Rhiannon / Tooth Fairy / 
Kiperina
There are some options, especially when it comes to Rhiannon's slot here. In the Star team, the flex slot is usually reserved for "targeters" (
Voyager, 
Regulus) who can direct [Impromptu Incantation] to target specific enemies using [Where The Stars Lead] and [Rockin' Spotlight] respectively. This is important because the Star version of [Impromptu Incantation] randomly changes its primary target with every attack.
Beyond that, AP-positive teamwide buffers like 
Mercuria or supports with high-profile debuffs like 
Argus' [Pinpointed] sometimes make an appearance.
However, recent developments show that there's a secondary type of team that can be created by combining the Afflatus drivers of the two Impromptu teams:
Impromptu Shotgun:
Paper Heron / Barcarola / Tooth Fairy / KiperinaThis is a team born from the unexpected interaction regarding Afflatus ownership.
If Barcarola is placed behind Paper Heron, [Impromptu Incantation] retains all the attributes it gains from [Qi Panorama] (e.g., frontloaded damage, fewer attack instances, Reality DMG) BUT its Afflatus changes into Star. This specific team is used in fights when frontloading damage is needed, as Barcarola’s only role here is to turn the Impromptu’s afflatus to Star. Do note that her ramping Crit buffs hardly do much in this case due to [Qi Panorama] forcing [Impromptu Incantation] to hit only up to 3 times (up to 5 with Paper Heron Portraits).
Here are some general rules of thumb when building your Impromptu team:
Having an Afflatus driver is extremely important to maximize the team’s damage. This comes in the form of Barcarola or Paper Heron (Limited).
If substituting in supports, choose supports that can provide teamwide buffing (e.g.,
Mercuria) or can inflict heavy debuffs on the main target (e.g., Argus ).Choose units that can quickly gather and expend [Eureka] to help charge [Inspiration] very quickly.
Ensure that all units are at relatively similar levels of investment. Investing heavily in one unit is a waste of resources because, again, [Impromptu Incantation] takes the average stats of the entire team.
Unit ranking
What follows are two tables, one displaying only characters that adhere specifically to the Impromptu Archetype. The other is a table of Generalist options, also ranked. Take note of the following:
Core — Integral to the functionality of the archetype.
Common — Most often seen in this position alongside the Core. Can be BiS.
Flex — Either good in specific situations or potentially good in a Common slot.
Cope — Only really used if nothing else is available. And even then, lmao.
Impromptu Unit Spread
Afflatus Driver | Support | Sustain | |
|---|---|---|---|
Core | | | |
Common | | ||
Flex |  | ||
Cope |
Core:
Paper Heron – Plant Afflatus Driver. Integral [Inspiration] generator with potent general offensive buffing and important Array.
Barcarola – Star Afflatus Driver. Integral [Inspiration] generator with potent Crit buffing.
Kiperina – Powerful AFK shielder, increases [Inspiration] cap and provides offensive (de)buffs.
Common:
Tooth Fairy (E1) – Important offensive debuffs (while relatively AFK) and AP buffs.
Aleph – Offensive (de)buffer with AP buffs and recasting allied cards. Used in Starpromptu.
Flex:
An-An Lee – Relatively AP-positive buffer and battery with offensive and defensive (de)buffs. Used in Plantpromptu.
Regulus (E1) – Targeter. Decent personal damage output. Used in Starpromptu.
Voyager (E1) – Targeter. Powerful defensive debuffs and crowd control. Used in Starpromptu.
Matilda (E1) – Decent Crit buffs for [Impromptu Incantation].
Cope:
N/A
Generalist Unit Spread
Damage Dealer | Support | Sustain | |
|---|---|---|---|
Core | |||
Common | | ||
Flex | |  | |
Cope |    |    |
Core:
N/A
Common:
Rhiannon – Generalist support with offensive (de)buffs and extra turn shenanigans. Her 0AP cards also allow for increased Inspiration funneling.
Flex:
Mercuria (E1) – Teamwide offensive buffing while requiring effectively no AP. Decent personal damage.
Argus (E1) – Very powerful offensive debuff, dispelling and decent personal damage output.
Fatutu – The frequent hits of [Impromptu Incantation] can provide extremely high healing numbers when attacking into a target affected by Fatutu's [Spirit Shell] and [Shell Beacon] debuffs.
Cope:
Charon – Teamwide offensive buffs with Enigma and [Pulsing Field]. Cannot be used with Paper Heron due to clashing Arrays.
Flutterpage – Consistent and high [Eureka] usage during her Ultimate allows her to function very comfortably as an [Inspiration] battery. However, [Impromptu Incantation] is not a FUA so she doesn't buff it.
6 (E1) – Can provide [Eureka] as well as many general (de)buffs.
Enigma – Great generalist sustain with offensive buffing alongside Charon. Cannot be used with Paper Heron due to clashing Arrays.