Under Night InBirth/UNI2/Damage and Combo System
Damage Scaling
As more attacks are added to a combo, each attack progressively does less damage due to damage scaling (also known as damage proration). To determine how much damage the second hit onwards (the first hit always deals 100% damage) in a combo will deal, there is a formula:
Damage = (Base Damage of the attack) × (Combo Rate × Distance Penalty) × (proration of all the preceding hits in a combo) × (bonus modifier)
 All the truncation happens after each multiplication and always round down, but cannot go under 1
The proration stacks multiplicatively. For example, for the third hit of a combo, proration = floor (proration of first hit × proration of second hit).
Proration Type  Description  Applies To 

Proration  Applied by every attack of a combo.

Next hit onwards 
Combo Rate  Applied 2nd hit onward. Everyone has 72% combo rate. Not all attacks will take Combo Rate into account (see below). 
2nd hit onwards 
Distance Penalty  Only applies when the distance between you and the opponent is more than 350 pixels, in which the formula is:
100  (Distance between you and the opponent  350) * 8 / 250 This number has a lower cap of 92. 
2nd hit onwards 
Bonus Modifier  A special modifier that applies under some circumstances.  Depends 
Bonus Modifiers
 Same Move Proration
 2A and 5A have a quality called Same Move Proration: canceling 5A/2A to itself will grant you an extra penalty proration. This penalty will repeatedly stack for each extra self cancel that hits.
Character  5A > 5A penality  2A > 2A penality 

Carmine, Vatista, Tsurugi  98  98 
Gordeau, Yuzuriha  97  98 
Everyone else  98  97 
 Smart Steer Ender
Damage for Smart Steer Ender is a little bit more trickier:
 Performing Smart Steer Ender by the Smart Steer combo will simply grant you a flat bonus proration that is character dependent:
Character  Bonus  Character  Bonus 

Hyde  110  Nanase  145 
Linne  91  Byakuya  168 
Waldstein  110  Akatsuki  153 
Carmine  130  Chaos  135 
Orie  150  Wagner  138 
Gordeau  115  Enkidu  138 
Merkava  108  Londrekia  155 
Vatista  128  Tsurugi  157 
Seth  145  Mika  146 
Yuzuriha  150  Kaguya  168 
Hilda  133  Kuon  153 
Eltnum  135  Phonon  150 
 Performing Smart Steer Ender directly instead will have a more complicated formula which is independent of character:
Bonus = [(Combo Point Bonus)  (Over Damage Penalty)] × (Distance Penalty)
Type  Description 

Combo Point Bonus  The more Combo Points you have, the higher the proration.

Over Damage Penalty  The more damage the combo already dealt, the lower the proration. This penalty only applies when the combo damage exceeds 1000, in which the formula is: Over Damage Penalty = 0.3 × (min{Combo Damage  1000, 1300} / 13) For example, performing Smart Steer Ender after doing a combo dealing more than 2300 damage will give you a 30 penalty. 
Distance Penalty  Only applies when the distance between you and the opponent is more than 350 pixels, in which the formula is:
100  (Distance between you and the opponent  350) * 8 / 250 This number has a lower cap of 85. 
Exceptions
Certain other mechanics can affect how much damage an attack or combo deals.
 Series of hits counted as 1 hit
 Most of the multihitting attacks (or a series of followups) are considered only 1 hit in the scaling. This has the most significance when it is the first hit of the combo, as all the hits of this move will not be affected by the Combo Rate. Such exceptions will be written by (1 hit) in the notes.
 Normal throw that GRD breaks
 Normal throws that cause a GRD break will have its base damage increased by 10%. Combined with the bonus damage (see below), a GRD break throw will deal 21% more damage than usual.
 Moves that ignores Combo Rate
 Certain moves ignores Combo Rate; that is, they never suffer from the 72% damage penalty when the move hits. This attribute can be found on all IWEXS moves, and only a handful of exceptions.
 Chain Shift
 Chain Shift when used in a combo increases the proration by 20% (multiply by 1.2). The result of multiplication cannot exceed 80.
Minimum Damage
All moves will do at least 1 damage at minimum. For certain moves however the minimum damage will change accordingly to deal a certain percentage of their original move damage; usually EX version of the specials and Infinity Worths have this property.
Despite the name "Minimum Damage" might suggest, the Minimum Damage will also scale depending on various situation:
Situation  Health > 30% or Health <= 30% but gain Vorpal during combos 
Health <= 30% 

2+ EX moves in a combo  50%  60% 
Second IW in a combo  30%  40% 
VeilOff^{[*]}  65%  80% 
Cross Cast VeilOff^{[*]}  60%  80% 
Combos starting from normal throws  80%  
Combos starting from invincible moves  60% 
 [*] Only applies to the current combo when VeilOff is activated.
When there are multiple possible penalties that can be applied, the penalty with the lowest value will be used.
 Exceptions
There are some special multipliers, all of them will stack multiplicatively if a previous penalty exists:
 Using an IW after using 2 EX moves in combos will give you a 120% bonus multiplier on the Penality. This means that EX > EX > IW in practice will deal 60% (72% if low health) Minimal Damage.
 Carmine's 22C (Launch!) has a 90% Penalty when move hits.
 Seth's j.214B (Piercing Penetration) has a 70% Penalty when move hits a blocking opponent.
Minimum damage is calculated after all normal combo scaling effects written above, but before bonus damage.
Bonus Damage
Vorpal, Celestial and Veil Off are the main ways to deal bonus damage. Those bonuses stack additively rather than multiplicatively.
Situation  Bonus 

Vorpal  +10% 
Celestial  +10% 
Opponent getting GRD Break  +10% 
Cross VeilOff  +20% 
VeilOff  +20% 
Combo Decay
As a combo goes on, the amount of hitstun each attack deals is reduced as it reaches certain thresholds. Hitstun/Untechable decay is determined by the moves that had used in the combo, as well as what starter is used. It is determined by the Combo Points, which can be calculated by the following formula:
Combo Points = (P1 of the first hit × Bonus Modifier) × (P2 of all the preceding hits in a combo except first hit)
 All the truncation happens after each multiplication and always round down, but cannot go under 1
Proration Type  Description 

P1  Apply if it is the first hit of the combo. 
Bonus Modifier  Modifier that applies to only P1 under certain circumstances. 
P2  Apply if it is not the first hit of the combo. Some multihit attacks will apply proration only once, regardless of how many hits connect, while some apply proration for each hit. 
Finally, this number (after multiplying P2 of the hit itself) is used to determine the decay of the hit:
Combo Points  Standing Hitstun 

X >= 35  0F 
29 <= X <= 34  1F 
24 <= X <= 28  3F 
19 <= X <= 23  4F 
14 <= X <= 18  5F 
10 <= X <= 13  7F 
6 <= X <= 9  10F 
3 <= X <= 5  14F 
X < 3  99F 
Every move also has a lower limit on the decay that will prevent the hitstun to decay further. This number is usually half of their hitstun (rounded up), so for example:
 A 14F hitstun move will have a minimum of 7F hitstun (so at max 7F);
 A 17F hitstun move will have a minimum of 9F hitstun (so at max 8F);
 A 19F hitstun move will have a minimum of 10F hitstun (so at max 9F).
Combo Points  Untechable 

X > 64  0F 
36 <= X <= 64  1F 
28 <= X <= 35  3F 
22 <= X <= 27  4F 
17 <= X <= 21  5F 
13 <= X <= 16  6F 
10 <= X <= 12  8F 
7 <= X <= 9  10F 
3 <= X <= 6  15F 
X <= 2  99F 
Every move also has a lower limit on the decay that will prevent the untechable to decay further, if met:
Moves  Untechable limit 

B air normals  6F 
B ground normals  7F 
C air normals  8F 
C ground normals  11F 
Other moves, Specials  Varies, usually half of their raw untech (rounded down) 
Cross Veil Off  999F? 
Special Modifers
 Bonus Modifier
 If the first hit is an Assault normal, the combo will have a 60% penalty.
 If the first hit is a Counter hit from moves that are not A normals, the combo will have a 120% bonus.
 Moves like 5A, 2A, j.A or any A normals (Low Breaks), will not receive this bonus.
 This will override the Assault penalty. In case of an Assault j.A, the Assault penalty will be removed, but does not apply the 120% bonus.
 If the first hit causes a GRD Break, the combo will have a 140% bonus. This will override the Assault penalty.
 Chain Shift
 Chain Shift when used in a combo increases the Combo Points by 50%.
 If you either possess more than 6 GRD blocks when Chain Shifting or you are in Celestial, Chain Shift increases the Combo Points by 70%,
The result of multiplication can never exceed 100 at any point.
 Cross VeilOff
Cross VeilOff increases the untechable depend on how many Combo Points you still have left:
Combo Points  Untechable 

X >= 64  +6F 
50 <= X <= 63  +5F 
38 <= X <= 49  +4F 
24 <= X <= 37  +3F 
12 <= X <= 23  +2F 
Cross VeilOff will not increase standing hitstun.
Special Combo limits
Wall/Ground bounces
Every combo has a limit of 3 Wall Bounces or Ground Bounce. When the limit is exhausted, the combo is forced to end.
Jump cancel
Every combo can only use a jump cancel once.
Increasing Hitstun
Crouching hit
Crouching opponents suffer 1F more hitstun compared to standing opponents  this can lead to new combo opportunities!
Counter hit
When a move counterhits the opponent, they experiences extra hitstop (in case of air hits, the untechable is increased) that allows you to combo into things where you usually can't when in normal hit. The extra hitstop depends on the types of moves, but generally they will do extra 23 frames of hitstop. Certain moves will also inflict special effects on counter hits.
While it doesn't increase the actual hitstun, it is more convenient to think that the extra hitstop gives extra hitstun on the first hit, as the hitstop only applies to them.