Note:
These functions are defined by Skript. You may also create your own functions! Tutorial for doing so is planned, but right now you need to seek it elsewhere.
Patterns: 

Since:  2.2 
Return Type:  Number 
Returns the absolute value of the argument, i.e. makes the argument positive.
Examples:
abs(3) = 3
abs(2) = 2
abs(2) = 2
Patterns: 

Since:  2.2 
Return Type:  Number 
Similar to atan, but requires two coordinates and returns values from 180 to 180. The returned angle is measured counterclockwise in a standard mathematical coordinate system (x to the right, y to the top).
Examples:
atan2(0, 1) = 0
atan2(10, 0) = 90
atan2(10, 5) = 63.4349
atan2(10, 0) = 90
atan2(10, 5) = 63.4349
Patterns: 

Since:  2.2dev32 
Return Type:  long 
Calculates the total amount of experience needed to achieve given level from scratch in Minecraft.
Examples:
Missing examples.
Patterns: 

Since:  2.5 
Return Type:  Boolean 
Checks if the contents of a list of strings are strictly equal with case sensitivity.
Examples:
caseEquals("hi", "Hi") = false
caseEquals("text", "text", "text") = true
caseEquals({some list variable::*})
caseEquals("text", "text", "text") = true
caseEquals({some list variable::*})
Patterns: 

Since:  2.2 
Return Type:  long 
Rounds a number up, i.e. returns the closest integer larger than or equal to the argument.
Examples:
ceil(2.34) = 3
ceil(2) = 2
ceil(2.99) = 3
ceil(2) = 2
ceil(2.99) = 3
Patterns: 

Since:  2.8.0 
Return Type:  Number 
Clamps one or more values between two numbers.
Examples:
clamp(5, 0, 10) = 5
clamp(5.5, 0, 5) = 5
clamp(0.25, 0, 0.5) = 0.25
clamp(5, 7, 10) = 7
clamp((5, 0, 10, 9, 13), 7, 10) = (7, 7, 10, 9, 10)
set {_clamped::*} to clamp({_values::*}, 0, 10)
clamp(5.5, 0, 5) = 5
clamp(0.25, 0, 0.5) = 0.25
clamp(5, 7, 10) = 7
clamp((5, 0, 10, 9, 13), 7, 10) = (7, 7, 10, 9, 10)
set {_clamped::*} to clamp({_values::*}, 0, 10)
Patterns: 

Since:  2.2 
Return Type:  Date 
Creates a date from a year, month, and day, and optionally also from hour, minute, second and millisecond. A time zone and DST offset can be specified as well (in minutes), if they are left out the server's time zone and DST offset are used (the created date will not retain this information).
Examples:
date(2014, 10, 1) # 0:00, 1st October 2014
date(1990, 3, 5, 14, 30) # 14:30, 5th May 1990
date(1999, 12, 31, 23, 59, 59, 999, 3*60, 0) # almost year 2000 in parts of Brazil (3 hours offset, no DST)
date(1990, 3, 5, 14, 30) # 14:30, 5th May 1990
date(1999, 12, 31, 23, 59, 59, 999, 3*60, 0) # almost year 2000 in parts of Brazil (3 hours offset, no DST)
Patterns: 

Since:  2.2 
Return Type:  Number 
The exponential function. You probably don't need this if you don't know what this is.
Examples:
exp(0) = 1
exp(1) = 2.7183
exp(1) = 2.7183
Patterns: 

Since:  2.2 
Return Type:  long 
Rounds a number down, i.e. returns the closest integer smaller than or equal to the argument.
Examples:
floor(2.34) = 2
floor(2) = 2
floor(2.99) = 2
floor(2) = 2
floor(2.99) = 2
Patterns: 

Since:  2.8.0 
Return Type:  Boolean 
Returns true if the input is NaN (not a number).
Examples:
isNaN(0) # false
isNaN(0/0) # true
isNaN(sqrt(1)) # true
isNaN(0/0) # true
isNaN(sqrt(1)) # true
Patterns: 

Since:  2.2 
Return Type:  Number 
The natural logarithm. You probably don't need this if you don't know what this is. Returns NaN (not a number) if the argument is negative.
Examples:
ln(1) = 0
ln(exp(5)) = 5
ln(2) = 0.6931
ln(exp(5)) = 5
ln(2) = 0.6931
Patterns: 

Since:  2.2 
Return Type:  Location 
Creates a location from a world and 3 coordinates, with an optional yaw and pitch. If for whatever reason the world is not found, it will fallback to the server's main world.
Examples:
location(0, 128, 0)
location(player's xcoordinate, player's ycoordinate + 5, player's zcoordinate, player's world, 0, 90)
location(0, 64, 0, world "world_nether")
location(100, 110, 145, world("my_custom_world"))
location(player's xcoordinate, player's ycoordinate + 5, player's zcoordinate, player's world, 0, 90)
location(0, 64, 0, world "world_nether")
location(100, 110, 145, world("my_custom_world"))
Patterns: 

Since:  2.2 
Return Type:  Number 
A logarithm, with base 10 if none is specified. This is the inverse operation to exponentiation (for positive bases only), i.e.
log(base ^ exponent, base) = exponent
for any positive number 'base' and any number 'exponent'. Another useful equation is base ^ log(a, base) = a
for any numbers 'base' and 'a'. Please note that due to how numbers are represented in computers, these equations do not hold for all numbers, as the computed values may slightly differ from the correct value. Returns NaN (not a number) if any of the arguments are negative. Examples:
log(100) = 2 # 10^2 = 100
log(16, 2) = 4 # 2^4 = 16
log(16, 2) = 4 # 2^4 = 16
Patterns: 

Since:  2.2 
Return Type:  Number 
Returns the maximum number from a list of numbers.
Examples:
max(1) = 1
max(1, 2, 3, 4) = 4
max({some list variable::*})
max(1, 2, 3, 4) = 4
max({some list variable::*})
Patterns: 

Since:  2.2 
Return Type:  Number 
Returns the minimum number from a list of numbers.
Examples:
min(1) = 1
min(1, 2, 3, 4) = 1
min({some list variable::*})
min(1, 2, 3, 4) = 1
min({some list variable::*})
Patterns: 

Since:  2.2 
Return Type:  Number 
Returns the modulo of the given arguments, i.e. the remainder of the division
d/m
, where d and m are the arguments of this function. The returned value is always positive. Returns NaN (not a number) if the second argument is zero. Examples:
mod(3, 2) = 1
mod(256436, 100) = 36
mod(1, 10) = 9
mod(256436, 100) = 36
mod(1, 10) = 9
Patterns: 

Since:  2.8.0 
Return Type:  Offline Player 
Returns a offline player from their name or UUID. This function will still return the player if they're online.
Examples:
set {_p} to offlineplayer("Notch")
set {_p} to offlineplayer("069a79f444e94726a5befca90e38aaf5")
set {_p} to offlineplayer("069a79f444e94726a5befca90e38aaf5")
Patterns: 

Since:  2.8.0 
Return Type:  Player 
Returns an online player from their name or UUID, if player is offline function will return nothing. Setting 'getExactPlayer' parameter to true will return the player whose name is exactly equal to the provided name instead of returning a player that their name starts with the provided name.
Examples:
set {_p} to player("Notch") # will return an online player whose name is or starts with 'Notch'
set {_p} to player("Notch", true) # will return the only online player whose name is 'Notch'
set {_p} to player("069a79f444e94726a5befca90e38aaf5") # &lt;none&gt; if player is offline
set {_p} to player("Notch", true) # will return the only online player whose name is 'Notch'
set {_p} to player("069a79f444e94726a5befca90e38aaf5") # &lt;none&gt; if player is offline
Patterns: 

Since:  2.2 
Return Type:  Number 
Calculates the product of a list of numbers.
Examples:
product(1) = 1
product(2, 3, 4) = 24
product({some list variable::*})
product(2, {_v::*}, and the player's ycoordinate)
product(2, 3, 4) = 24
product({some list variable::*})
product(2, {_v::*}, and the player's ycoordinate)
Patterns: 

Since:  2.5 
Return Type:  Color 
Returns a RGB color from the given red, green and blue parameters.
Examples:
dye player's leggings rgb(120, 30, 45)
Patterns: 

Since:  2.2, 2.7 (decimal placement) 
Return Type:  Number 
Rounds a number, i.e. returns the closest integer to the argument. Place a second argument to define the decimal placement.
Examples:
round(2.34) = 2
round(2) = 2
round(2.99) = 3
round(2.5) = 3
round(2) = 2
round(2.99) = 3
round(2.5) = 3
Patterns: 

Since:  2.2 
Return Type:  Number 
The sine function. It starts at 0° with a value of 0, goes to 1 at 90°, back to 0 at 180°, to 1 at 270° and then repeats every 360°. Uses degrees, not radians.
Examples:
sin(90) = 1
sin(60) = 0.866
sin(60) = 0.866
Patterns: 

Since:  2.2 
Return Type:  Number 
The square root, which is the inverse operation to squaring a number (for positive numbers only). This is the same as
(argument) ^ (1/2)
– other roots can be calculated via number ^ (1/root)
, e.g. set {_l} to {_volume}^(1/3)
. Returns NaN (not a number) if the argument is negative. Examples:
sqrt(4) = 2
sqrt(2) = 1.4142
sqrt(1) = NaN
sqrt(2) = 1.4142
sqrt(1) = NaN
Patterns: 

Since:  2.2 
Return Type:  Number 
Sums a list of numbers.
Examples:
sum(1) = 1
sum(2, 3, 4) = 9
sum({some list variable::*})
sum(2, {_v::*}, and the player's ycoordinate)
sum(2, 3, 4) = 9
sum({some list variable::*})
sum(2, {_v::*}, and the player's ycoordinate)
Patterns: 

Since:  2.2dev23 
Return Type:  Vector 
Creates a new vector, which can be used with various expressions, effects and functions.
Examples:
vector(0, 0, 0)