Update 1.9

Update 1.9 was the ninth major update to Geometry Dash. It was officially released to the public on November 9, 2014. As well as introducing two new levels, Blast Processing and Theory of Everything 2. The Wave game mode made its debut here, appearing in both the aforementioned levels. The custom song function was also introduced, allowing players to use songs from the audio-sharing website Newgrounds in their custom levels.

Previews
Prior to the release of Update 1.8, Topala said in a conversation at Touch Arcade Forums, "I have a lot of ideas for Update 1.9 that could be huge for the game, but more on that after I release 1.8... muahaha!"
 * August 13, 2014: Topala posts his first Update 1.9 preview image, which shows five icons wearing different-colored headphones. This makes way for much anticipation throughout the Geometry Dash community and results in theories involving soundtrack changes within a level and new game modes.
 * August 26, 2014: Topala publishes another image depicting three-dimensional blocks, arousing much excitement among Geometry Dash players.
 * August 28, 2014: Topala continues with the three-dimensional idea, posting a picture on Facebook about what could be built using the blocks.
 * September 6, 2014: Another image is posted through Topala's social media accounts, featuring several different map components that could be used in future Geometry Dash levels. This includes two new icons, gear-like obstacles, and various different unknown types of blocks. The most prominent feature is a new thick blue portal that would likely result in the introduction of a new game mode.
 * September 14, 2014: Topala posts another image to social media, hinting the soundtracks for the upcoming levels. It has a blast and processor (which was later confirmed to be Blast Processing by Waterflame) and a book, an infinity symbol, and the number 2 (which in truth hinted to Theory of Everything 2 by DJ Nate). The latter was correctly theorized to be a demon level, following similar lines to Update 1.6.
 * September 21, 2014: Another image is posted through Facebook and Twitter. It previews a new custom music feature that would allow players to include music from Newgrounds in their custom levels. The image includes ten icons with headphones at the bottom. It is the first picture to indicate that the update was a work in progress. Upon the release of the image, Topala says that a sneak peek video for the next levels would be coming soon.
 * September 28, 2014: Topala officially releases the first Update 1.9 sneak peek video, which shows the first 21 seconds of a beta version of Blast Processing. As seen in the video, the new blue portal changes the icon to an arrow-like object with physics similar to those seen in the mobile game, Wave Wave.
 * October 10, 2014: Topala releases another sneak peek video featuring the second level, Theory of Everything 2. In this video, a new background and a new design of ship is used. Topala is also playing the game on his computer, indicating that he may have been using the future Steam version.
 * October 18, 2014: Topala confirms that the update would be released soon after he had fixed a minor issues in the backup and music systems. He also says he is working on the Steam version, and hints on Update 2.0, stating that he will continue improving the user account system devised in 1.9.
 * November 4, 2014: Topala posts that the update is submitted for review and is waiting to be accepted.
 * November 9, 2014,: Nearly three months after Update 1.9 was first mentioned, Topala confirms the release of 1.9 and states that it will be released to iOS and Android devices around the same time, and the Steam version would be released as soon as possible.
 * November 13, 2014: Update 1.9 is released to the Windows Phone, App Store, and several other mobile devices.
 * November 14, 2014: Update 1.91 is released to all devices. This is a minor update that fixes a few bugs.
 * November 15, 2014: Update 1.9 is released on Amazon devices.
 * January 18, 2015: Update 1.92 is released to the Play Store. This includes some new options and fixes a few custom soundtrack bugs.
 * February 12, 2015: Update 1.93 is released to the Play Store. This is a minor update that includes some bugfixes.
 * February 16, 2015: Update 1.93 is released to App Store.

Introductions

 * New level "Blast Processing".
 * New level "Theory of Everything 2".
 * New "Wave" Game mode.
 * New music system. Build and share levels using custom music from Newgrounds.
 * Lots of new details and level objects.
 * (Not fully functional) Everyplay support for Android.
 * Customize the color.
 * Color coding in editor to make different objects more clear.
 * New search options.
 * Improved server performance for downloading levels.
 * Copy/paste support in editor. (not duplicate, paste object anywhere in the level).
 * Level editor object limit increased to 15,000 (in 1.92 and PC version - 20,000)
 * The 99% achievement got nerfed to dying between 95% and 99%, making it possible to get the achievement in all main levels (including Lite ones), not just Electrodynamix and Hexagon Force.
 * A lot of difficulties for levels have been changed: Back on Track now is Easy, Polargeist and Dry Out now are Normal, Base After Base and Can't Let Go now are Hard, Jumper, Time Machine and Cycles are now Harder difficulty.
 * A new sound engine was introduced.
 * Stereo Madness's third coin was given a less difficult path.
 * The game now automatically names your level "Unnamed 0" when you don't set a name for it. Your second unnamed level will be named "Unnamed 1", your third unnamed level will be named "Unnamed 2", and so forth.
 * A new secret achievement was added (Master Detective!)
 * When creating a level with the same name as another level in your edited levels list, It will add Rev 1 in gold text, If you make another level with the same name It will say Rev 2 and Rev 3 and so forth.

Update 1.92

 * New option that can help reduce lag on some devices ("options/smooth fix") & Other few new Settings options.
 * Added group features to level editor. (Ability to separate Objects with Groups)
 * Max objects increased to 20,000.
 * Custom song bugfixes.
 * Steam users can now use their exclusive icons in the mobile version.
 * Random bugfixes and tweaks.

Update 1.93

 * Bugfixes and tweaks

Geometry Dash Lite Introductions
On February 5, 2015, Geometry Dash Lite was updated straight to version 1.921, which included the following:
 * New level "Time Machine"!
 * New achievements and rewards!
 * Account system
 * Bugfixes and tweaks

Trivia

 * The new arrow-like form, known as the Wave, was inspired by the mechanics of the mobile game Wave Wave. It is supposed the concept was brought to light by a popular Geometry Dash player, TheRealDarnoc, who created a level (also named Wave Wave), mimicking its mechanics using condensed groups of gravity rings and the UFO.
 * This is the first update to include a sequel of a main level song: Theory of Everything - Theory of Everything 2
 * This is the second update that includes two new main levels. (1.6 with Electroman Adventures and Clubstep, and now 1.9 with Blast Processing and Theory of Everything 2.)
 * Both Update 1.6 and Update 1.9 featured music from both Waterflame and DJ Nate.
 * This update included a notably smaller amount of new customizations, even when including the Steam exclusive icons.
 * The update 1.92 came along with a bug that is still being abused and it's the ability to finish a level without completing it and you delete it instead. It consists on holding the "Play" button and pressing the "X (Delete)" button and press "yes" at the same time you stop pressing the play button. The level will delete itself and you'll finish it, it looks like an empty level except for the difference that you get the stars the level is given. This results in a ban (permanent) if abused or gets noticed.
 * The Top 100 is now filled with people who have abused this bug. However, Robtop is banning those people from the leaderboards from time to time.
 * When 1.9 was released, you could get all the coins and reach a lot of stars by merging two accounts in one. This would happen if you had progress in an account and logged into another in the same device and loaded the progress with the older one running on the background; this would result in an account merge and the progress would sum.  This wouldn't result in a ban from the leaderboard. 
 * Blast Processing has the most differences between the official level and the sneak peek, all of which are decoration-related.
 * At a later time Robtop enabled a feature that unfeatured all levels with copyrighted music.

Links

 * https://www.youtube.com/user/RobTopGames (YouTube Channel)
 * https://www.facebook.com/geometrydash (Facebook Account)
 * https://twitter.com/RobTopGames (Twitter Account)
 * http://forums.toucharcade.com/showthread.php?t=203823 (Touch Arcade Forums)