Sonic Wave is one of the most historically important Extreme Demons in Geometry Dash. For a long time it sat near the very top of the difficulty list, and its name became shorthand for "the wall" of GD difficulty.
The level is best known for its long, narrow wave sections that demand pixel-precise control. It has spawned numerous remakes, sequels (most famously Sonic Wave Infinity), and a place in nearly every conversation about top-tier difficulty.
Soundtrack
♪ Sonic Blaster — Waterflame