15 degree patterns is a slider exclusive technique.
You start off by mapping a section with only horizontal and vertical sliders.
Then rotate them 15 degrees clockwise or anti-clockwise.
This basically adds a more style to a group of sliders.
Angles between 10 and 80 degrees can also be used.
Ctrl+ clicking on them or by dragging along the timeline.
Edit(near the top left) then
15(or any number between 10 and 80) in the text box.
Anti-Clockwise, it doesn't really matter.
Not to be confused with Spacing Out.
Accelerated spacing is where the distance of each hit object is placed farther and farther apart, while the timing between them remains the same.
Back and forth beats are comprised of two stacks of beats (or more), with the odd notes in one stack and even notes in the other.
Using this requires the player to alternate between the two stacks.
It is encouraged to only be used for harder difficulties as this can be hard for newer players.
Differential stacks consist of notes that are spaced apart inconsistently from each other in the timeline.
A notable thing is that these objects are mapped as if they are a consistent beat.
Some sightreading may be required unless you can really follow the music.
When playing a beatmap using this technique, it can be very challenging to play with the hidden game modifier.
Drain sections is a section in a beatmap that suddenly becomes slower or less difficult in an attempt to either match the song better or cause the HP bar to drain.
This can be done by placing less notes and/or slowing the slider speed.
Drain sections should be used sparingly and only when the song may hint it.
Half-Backing is comprised of a quarter beat followed by two-eighth beats, arranged similarly to back and forth beats except the third note stops.
This will create a straight line.
The hub and spoke formation is literally a hub with spokes peaking out.
This technique requires at least 8 to 9 hit objects that are half a beat apart from another.
Using this will force the player to not only move in a circular direction but also require them to return back to the centre after an object was hit.
In general, this is basically the QQ diamonds technique with a centre for every other hit object.
First, place the odd numbered combos in the centre of where the hub and spoke is to be mapped (this part is the "hub").
The following, even, hit objects are to then be placed 0 degrees, 90 degrees, 180 degrees, 270 degrees (or vice versa) surrounding the "hub" (these are the "spokes").
It is very important to lay the hit objects out so that they go in a clockwise or counterclockwise direction.
The basic form of the Hub and Spoke uses 4 spokes.
You could, however, use 3, 5, or 6 spokes instead (when you do this, make sure that the degree measure remains equal for each spoke).
Linear back and forth is a variation of the back and forth beats spreads.
The difference is that there these don't use stacks rather, they require the player to move along back and forth between the hit objects.
It is very important that the mapper makes it clear as to the direction of where the spread is heading.
Not to be confused with Accelerated Spacing
Spacing out refers to hit objects in which they are placed distance-wise, not time.
This technique has the advantage of keeping a momentum in a tune running during that section of a map.
However, incorrect patternmapping can lead to an almost unplayable map.
Basically, form a square around the centre with 4 hit circles.
The next 4 hit circles are then to be placed 1 grid space outwards and so on.
Another varient you can add is to place a hit circle in the centre after each cycle.
Step-Too-Fars uses a linear path of hit circles that are a quarter beat apart.
However, upon hitting the "end" of the line, the hit objects moves back one space (the hit circle before the line had ended) then changes direction.
Slider slowdowns abruptly slows down a slider by temporarily halving an inherited timing point (the green ones) to complement the music's (or vocals') long note.
See Mapping techniques/Basics for a description on streams.
Compressed streams uses hit circles that are only 3 grid spaces apart (on a 2 or 3-grid level).
Otherwise, just make the stream considerably smaller compared to the rest of the map.
A majority of maps that uses streams are most likely to be seen using compressed streams.
Discontinuous streams is when there is a jump in the stream even if the timing between the notes in the jump are the same length as the timing between notes in the rest of the stream.
Deathstream are very long and difficult streams.
These consist of sliders (with or without repeats), hit circles or a combination of both.
The job of a deathstream is to practically fail players that cannot handle ordinary streams.
The use of deathstreams will make your map unrankable!
However, it may go through as one of the approved beatmaps.
Slider stream jumps is a more advanced technique for osu!.
Instead of using an orthodox stream, you replace it with sliders.
This keeps the same stream difficulty, as you need to move and click rather than just following a stream.
Essentially, you jump with your cursor and stream, hence the term Slider Stream Jumps.
Triplet Streams uses a set of three hit circles that requires to be tapped in a quick succession.
These are commonly placed in a 1/4 beat snap divisor depending on BPM of the map.
They can come in a single succession or multiple depending on what the mapper wishes.
Note, Triplet Steams does not refer to an actual triplet in music theory.
Variable spaced streams use longer streams with inconsistent distance snap (usually increasing).
Zig-Zag streams are streams with hit objects placed in such a manner that they form a very jagged line.
However, they are placed very closely that they can be passed by moving the cursor through them in a straight line which intersects all notes.
These are most commonly found with notes zig-zagging across one another.