Attributes

Attributes, also known as stats, are the numerical values of a character that affect his performance and the behavior of his tears, the game primary weapon. All characters start with a different set of values and they can be increased or decreased during a run.
Most stats can be viewed on the pause menu, except for health (which is shown in the game HUD) and shot height (which is a hidden attribute). Multiple items increase or decrease stats by a decimal value, but the game menu only show stat changes for integer values, on a scale graded from 0 to 7.

Health

Damage

Tears

Range

Shot Speed

Speed

Luck

Hidden Attributes

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Health represents the amount of damage the player can take before dying. There are four different types of health in the game, each with their own pickups. The health bar is the visual representation of a player's health on the HUD.

• The order in which hearts are placed is, from left to right, Red Hearts (and empty containers), Eternal Hearts, then Soul Hearts or Black Hearts (depending on the order in which they were picked up).
• Hearts are generally lost from right to left: Last grabbed Black/Soul hearts, Eternal Hearts, then Red Hearts.
  • The exception to this rule are self-damaging items like Razor Blade, Devil Beggars and Blood Donation Machines, which always prioritize heart containers. From these sources, health is lost in the following order: Eternal Hearts, Red Hearts, then Soul/Black hearts.
• The character can only hold a maximum of twelve hearts, and any permutation of the four different types can be used. Picking up a Black or Soul heart will refill a halved Black/Soul heart (the other half is then placed at its right); Soul Hearts can replenish Black hearts and vice versa.

Heart Containers

Heart Containers, or Red Hearts, are the main form of health for the majority of characters. If the player has only Red Hearts, the containers will be unfilled as damage is taken (but the containers themselves remain). Empty Heart Containers can be refilled with red heart pickups. The number of heart containers can be increased with multiple items or Health Up pills or decreased with items, Health Down pills, having another player join a game as a baby, or trading them away in a Devil Room or at an underground Black Market.

Soul Hearts

Soul Hearts are blue hearts that are appended to the end of the health bar. Unlike red hearts, soul hearts do not have containers, so once they're depleted, new ones must replace them. Losing soul hearts does not count as damage for the purposes of Devil Room or Angel Room appearance chances, but does count as damage taken for the achievements Basement Boy, Spelunker Boy, Dark Boy, and Mama's Boy.

Black Hearts

Black Hearts are similar to Soul Hearts in that they are appended to the end of the health bar, are not permanent, and that losing them does not count as damage for the purposes of Devil or Angel Room chances. However, when a Black heart is depleted, The Necronomicon's effect is triggered, damaging all enemies in the current room. If the player already has twelve hearts, picking up a Black heart will only add it to the health pool if the player has at least one soul heart, in which case the Black Heart replaces the Soul Heart.

Eternal Hearts

Eternal Hearts are the rarest variation of a heart. They always appear as half-hearts and, once picked up, can transform into a new heart container in two ways: either by collecting a second Eternal Heart in the same level, or by traveling to the next floor. Eternal Hearts are not permanent, cannot be refilled when lost and do not count for the limit of twelve hearts, instead overlapping the rightmost red heart container. If no heart containers are available, the eternal heart will take the place of the leftmost soul heart or black heart. Health removal from Devil Room deals will not drain an Eternal Heart; rather, the Eternal Heart is appended onto the end of the next red heart.

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Damage refers to the amount of damage each tear deals to enemies, and is represented by a sword. As damage increases, the size of the tears increases as well. However, tear size is not always a valid indication of how much damage your tears will do. Tears will grow and shrink when your damage changes, but tears of a certain size do not have a specific damage value, and two tears of the same size (in two different runs) are likely to have different damage values.

• Polyphemus is an example of an item which provides a very high Damage stat.

Effective Damage

The formula for damage, as defined by a user named Twinge:

File:Effective Damage Formula.png

where:

• CharBaseDmg = 3.5 multiplied by a particular Character Modifier,
• TotalDmgUps = the total of all regular damage ups collected (not including special exceptions or damage multipliers),
• FlatDmgUps = the total of all damage ups that are excluded from the above (for example, Curved Horn or Ipecac), and
• EffectiveDmg = the approximate damage that can be expected per tear, or per 'tick' when using Brimstone or Technology 2.

There does not seem to be any particular pattern to what defines a Flat Damage Up, nor is it made obvious within the game. However, they can be determined through testing.

Taken from [Twinge's spreadsheet]: "This is a logrithmic formula that makes most Damage Ups more potent the less you have. For example, if you have a Pentagram on Isaac, your total damage would be (1 * 1.2 + 1)^0.5 = 1.48 * 3.5 = 5.19. Another damage up increases this to 6.45 (a 1.26 increase instead of a 1.69 increase). Adding a Curved Horn simply adds the damage at the end, so it becomes 8.45. The higher a character's base damage, the more effective Damage Ups will be for that character. Special adjusts like Polyphemus or Sacred Heart happen after the main formula."

Character Modifier

The character base damage of each tear is calculated multiplying the base damage of 3.50 with each character's damage modifier. These character modifiers are:

• Eve^†: 0.75 • 3.50 = 2.625 per tear
• Isaac, Magdalene, Samson, Lazarus, Eden, and The Lost: 1.00 • 3.50 = 3.50 per tear
• ???: 1.05 • 3.50 = 3.675 per tear
• Cain and Revived Lazarus: 1.20 • 3.50 = 4.20 per tear
• Judas: 1.35 • 3.50 = 4.725 per tear
• Azazel: 1.50 • 3.50 = 5.25 per beam tick.
• Black Judas: 2 • 3.50 = 7.00 per tear

^†: Whore of Babylon has the unique effect of increasing Eve's damage modifier from 0.75 to 1.00 when active. This does not apply to other characters, however.

Damage Multipliers

Some items multiply your damage rather than simply adding to it. Damage multipliers do not simply multiply your current damage once; your damage stat is constantly recalculated and the damage multipliers are multiplied with the end result. This means that if you start with 3.50 damage and get a 2x multiplier, your effective damage will be 3.5*2 = 7.00. If you then pick up a +1 damage, your effective damage will be 3.5*(1*1.2+1)^0.5*2 = 3.5*(2.2)^0.5*2 = 3.5*1.48*2 = 10.38, and not 7.00 + 1.

Due to the nature of the game's programming, some damage multipliers do not stack with each other. For example, Cricket's Head and Magic Mushroom both provide a damage multiplier of 1.5x. If you were to pick them up, you would expect the total multiplier to be 2.25x, but in reality the total multiplier is still 1.5x. This problem will also occur with the 1.5x multiplier provided by having both Blood Of The Martyr and The Book Of Belial.

On the other hand, most damage multipliers DO stack. For example, Proptosis and Eve's Mascara both provide a 2x multiplier, and picking up both will give you a total multiplier of 4x.

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Template:DisambigMsg The Tears attribute determines the rate of fire of the character, and is represented by 3 arrows. This attribute is also known as the tear delay (the delay between successive shots, as opposed to the inverse 'tears per second'); a higher tears stat means a shorter delay.

Tear Delay

The formula for tear delay is: File:Tear Delay Formula.png

TotalTears is equal to the normal tears stat. For example, picking up Sad Onion would grant 0.7 TotalTears, making Isaac's tear delay 7.7 which is rounded down to 7.

Several items directly modify tear delay after this main calculation:

• Anti-Gravity: -2 tear delay
• Cancer (Trinket): -2 tear delay
• Capricorn: -1 tear delay
• Chocolate Milk + The Ludovico Technique: -1 tear delay
• Cricket's Body: -1 tear delay
• Dr. Fetus: tear delay * 2.5
• Template:Afterbirth Epiphora: tear delay / 2 (while at max "charge")
• Eve's Mascara: tear delay x 2
• Guillotine: -1 tear delay
• Ipecac: (tear delay x 2) + 10
• Template:Afterbirth Milk!: -2 tear delay (after taking damage for the current room)
• Mom's Perfume: -1 tear delay
• Mutant Spider: (tear delay x 2.1) + 3
• Pisces: -1 tear delay
• Polyphemus: (tear delay x 2.1) + 3
• Template:Afterbirth Purity: -4 tear delay while blue aura is active
• Soy Milk: (tear delay / 4) - 2
• The Inner Eye: (tear delay x 2.1) + 3

The minimum tear delay that can be reached with regular tears up items is 5, but with items that directly reduce tear delay, tear delay can reach a minimum of 1.

The number of tears per second that the player fires is found by the formula: File:Tears Per Second Formula.png.

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Range determines how long tears will travel before landing, and is represented by a bow and arrow. Effective range is determined by a combination of the Range stat, Shot Speed, and Shot Height.
This attribute's name is misleading, because Range actually determines the time that a shot stays in the air rather than the "distance" that it travels. The effective range is calculated based on said travel time, shot speed, and shot height.

Different characters start with varying range:

• Isaac, Magdalene, Judas, ???, Eve, The Lost, and Black Judas: 23.75
• Cain, Azazel and Lazarus: 17.75
• Samson: 18.75
• Revived Lazarus: 28.75

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Shot Speed is the attribute that governs how quickly an individual tear travels, and is represented by a speeding ball. Shot Speed also affects the effective range of the tears. As the range stat determines how long tears will stay in the air (and not distance traveled), a lesser shot speed reduces effective range.

All characters start with the same shot speed except for Samson, who has a 31% increased shot speed, and Eden, whose shot speed can be anywhere between 75% and 125%.

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Speed determines how quickly the character moves, and is represented by a shoe. Speed has a minimum value of 0.1 and a maximum value of 2.0. Different characters start with varying speeds:

• Isaac, Judas, Lazarus, and The Lost: 1.0
• Magdalene: 0.85
• Cain: 1.3
• Eve: 1.23
• ???, Samson, and Black Judas: 1.1
• Azazel and Revived Lazarus: 1.25

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Luck affects a variety of chance-based effects and is represented by a 3-leaf clover.
Each Luck-affecting item (Luck Up pill, Lucky Toe, Lucky Scab,...) gives +1 Luck to the character (Luck Down is -1 Luck).
Luck influences many different elements:

• Room drops: Higher Luck gives a higher chance on drops after clearing rooms, going up to 100% guaranteed drops on any room at around 3-4 Luck in Normal Mode, and less than 10 Luck on Hard Mode.
  
  • The chance of chest drops is also greatly increased (and gives chests nearly every time when combined with Guppy's Tail).
• Tear effect chance: The chance of shooting tears with status effects becomes more likely as Luck goes up. This scales up to 100% chance per tear in most cases with enough Luck.
  • Most of the status inflicting effects require a very unlikely high number of Luck to activate on every tear.
    • Since these effects persist on the enemies for a set amount of time regardless of the Tears stat, a fast rate of fire is often enough to affect an enemy indefinitely.
  • Tear items affected by Luck are:
    • Mom's Eye (Front and back tears) - 100% at 2 Luck
    • Loki's Horns (4-way tears) - 100% at 7 Luck
    • Tough Love (Teeth instead of tears) - 100% at 9 Luck
    • Mom's Wig (Friendly spiders while shooting) - 100% at 10 Luck
    • The Common Cold (Poison tears) - 100% at 12 Luck
    • Fire Mind (Fire tears) - 100% at 13 Luck
    • Spider Bite (Tears slow enemies) - 100% at 15 Luck
    • Ball of Tar (Tears slow enemies) - 100% at 18 Luck
    • Mom's Contacts (Tears freeze enemies) - Maximizes at 50% with less than 20 Luck
    • Dark Matter (Tears cause fear) - 100% at 20 Luck
    • Iron Bar (Tears confuse enemies) - 100% at 27 Luck
    • Mom's Eyeshadow (Tears charm enemies) - 100% at 27 Luck
    • Abaddon (Tears cause fear) - 100% at 85 Luck
    • Mom's Perfume (Tears cause fear) - 100% at 85 Luck

• • Trinkets affected by Luck are:
    • Pinky Eye (Poison tears) - 100% at 18 Luck
    • Push Pin (Spectral + Piercing tears) - 100% at 18 Luck
    • Cartridge (Gamekid effect when hit) - 100% at 38 Luck
    • Samson's Lock (chance for +0.5 Damage Up when kill) - 100% at 10 Luck
    • A Missing Page (Necronomicon effect) - Maximizes at 50% with 50-60 Luck
• Celtic Cross: The Celtic Cross grants its invulnerability more often with higher Luck, topping out at 100% at 27 Luck.
• Virgo: The shield activation chance increases with Luck, topping out at 100% at 10 Luck.
• Gimpy: The Soul Heart/Black Heart drop chance upon taking damage increases with higher Luck, topping out at 50% at 22 Luck. However, due to a programming error, Gimpy won't drop any Soul/Black Hearts if you have more than 22 Luck.
• Old Bandage: The Red Heart drop chance when you take a hit increases with higher Luck, topping out at 50% at 29 Luck. However, due to a programming error, Old Bandage won't drop any Red Hearts if you have more than 29 Luck.
• Midas' Touch: Poops have a chance to turn in Golden Poop. That chance increases with higher Luck.
• Slot Machine: Slot machines pay out more often with higher luck, but doesn't scale up to 100% payout chance. The increased payout chance is, however, enough to make the machine almost definitely profitable, and Pretty Fly is awarded more frequently.
• Shell Game: Shell games pay out more often with higher luck, but doesn't scale up to 100% payout chance. The increased payout chance is, however, enough to make the beggar almost definitely profitable.
  

However, Luck doesn't affect:

• Fortune Teller and Portable Slot: Unlike Slot Machines, their chance of giving a consumable don't increase with Luck. Only Lucky Foot increases the winning chances with these machines.
• The activation chance of: Fanny Pack, Dry Baby, Mulligan, Broken Watch, Infamy, Tech.5, Guppy's Collar, Undefined (for ERROR Room or Black Market teleports), We Need To Go Deeper! (for Trapdoor rooms), Pandora's Box (as its effects are predetermined depending on which floor it's used on), and Missing Page 2.
• Content from Chests, Pots, Mushrooms, Skulls, Blue Fires, Purple Fires, Devil Rooms, and Angel Rooms.
• Normal Beggars, Devil Beggars, and Key Masters aren't affected by Luck.

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Shot Height

Shot Height is a hidden attribute that determines how far above the ground tears travel. A greater Shot Height effectively increases range, and a high enough Shot Height can allow tears to fly over obstacles without spectral tears. Tiny Planet greatly increases shot height, allowing tears to travel above obstacles.

Knock-back

Knock-back (or knockback) is a mechanic that determines how far an entity is pushed back by a certain force.

There are two kinds of knock-back: directional and circular.

Directional Knock-back

This knock-back comes from Tears, most notably Isaac's. The knock-back force is determined by the speed and direction of the tear, which itself is determined by Isaac's movement and stats. (Needs research and confirmation)

Directional knock-back affects most enemies, including bosses (except for stationary ones like Pin or Round Worm). Items (both Trinkets and Pickups) cannot be moved by tears.

Notes

• Piercing shots from items like Sagittarius or Cupid's Arrow will remove the knock-back from tears.
• Knock-back from tears provides minor crowd control for homing enemies like flies or Gapers, increasing the time it takes them to reach Isaac.
• Be wary of the natural knock-back from tears when trying to dodge charging enemies (like the smaller twin of Gemini, Gurglings, and Leeches): The tears can push them off-track and and towards the direction you are planning to escape to.

Circular Knock-back

This knock-back is a little shockwave that's emitted at a certain radius in all directions, most prominently from explosives, like Bombs.
Certain farts also create a (non-harmful) knock-back. Some enemies, like the Fatty, can fart, and Isaac can also do so with the Butter Bean.

Pickups (including Chests) are affected by circular knock-back; items, however, are not.

Notes

• There is also a mechanic that acts as an opposite of sorts to circular knock-back: a gravitational pull that is emitted from Gaping Maws, Mega Fatty (while charging up its "Vomit Storm" attack), purple Champion monsters, and magnetic tears.

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