Update 1.6 introduced Electroman Adventures and this level, which was the first to be introduced of its difficulty.
Clubstep
Name 2/3 of the levels that currently make up the top 3 on the Geometry Dash Demonlist.
Tidal Wave, Acheron, Silent Clubstep
Which 3 levels made up the original RGB trilogy?
Yatagarasu, Sonic Wave, and Erebus
This main level was the hardest in the game upon release of version 1.0
Jumper
This extreme demon is the oldest level currently on the Demonlist.
Silent Club
This was the first demon level to be created in Geometry Dash.
Demon Park by M2col
How many secret coins does it take to unlock Clubstep, Theory of Everything 2, and Deadlocked respectively?
10, 20, and 30.
This extreme demon, who's rating was considered to be controversial, was created during 2.0 and considered impossible until its verification during 2.1.
Thinking Space by HidekiX, verified by Atomic
These 2 Extreme Demons, which were in the process of being created in 2018, were well known throughout the community and were in consideration to be some of the best decorated levels for their time.
Astral Divinity (then known as God Eater,) and Woodkid
There are this many main levels rated insane.
8
This was the first extreme demon to be legitimately completed by a human.
Cataclysm by Ggboy
Geometry Dash 1.3 added this gameplay mechanic.
Blue orbs/pads
This music artist made the song for Polargeist.
Step
This extreme demon was top 1 at the time of its verification, but ended up being placed at #2 on the list due to when it got rated.
Crimson Planet or Firework
This YouTube channel is known for creating the video that popularized the joke "does this look possible to you at 100% speed?"
TheMuteTroll