1. Introduction of the Game:
Geometry Dash SubZero is an electrifying side-scrolling platformer that challenges players with rhythm-based levels, each crafted to test their reflexes and timing. Developed by RobTop Games, this installment of the wildly popular Geometry Dash series offers a distinctive blend of music and fast-paced action, where players must navigate through treacherous obstacles to the accompaniment of pulsating electronic soundtracks.

2. All Characters and Levels of the Game:
In Geometry Dash SubZero, players do not pick from different characters but instead control a customizable icon, typically referred to as the cube. As they progress through the game, they can unlock and choose various skins and effects for their icon. The game features three main levels: "Press Start," "Nock Em," and "Power Trip." Each level has a unique soundtrack and visual theme and offers different challenges, ensuring a fresh experience for every stage.

3. What Attracts Users Most to the Game:
Players are drawn to Geometry Dash SubZero by its engaging yet simple gameplay, which requires just a tap to jump, fly, or flip through the levels. The vivid, neon visuals combined with a compelling electronic soundtrack create an immersive experience. Furthermore, the game's reputation for having a challenging difficulty level adds a sense of accomplishment upon completing each stage.

4. Why It Is Popular:
Geometry Dash SubZero has amassed a loyal fanbase due to its distinctive combination of addictive gameplay, precision-based challenges, and captivating audio-visual design. The series has a strong community of dedicated players who not only play the levels but also create and share their own using the game's level editor. This aspect of creation and community involvement has contributed significantly to its popularity.

5. When the Game Was Released and How Many Versions Are Currently Available:
Geometry Dash SubZero was released on December 21, 2017. It is a standalone game under the Geometry Dash brand, complementing other titles like the original Geometry Dash, Geometry Dash Lite, Geometry Dash Meltdown, and Geometry Dash World. There is currently only one version of Geometry Dash SubZero, barring updates that have been released for the game.

6. The Most Difficult Part of the Game:
The most daunting part of the game tends to be the precise timing and rapid reflexes required to navigate through the levels, especially when the gameplay speeds up or when players encounter complex sequences of obstacles. Each level introduces new elements and mechanics, keeping players on their toes and testing their dexterity to the fullest.

7. Strengths and Weaknesses of the Game:
The strengths of Geometry Dash SubZero include its captivating soundtrack, vibrant visuals, and addictive gameplay that continually challenges the player's skills. However, its weaknesses might be rooted in its high difficulty level, which can be off-putting for some casual players or those prone to frustration. The game can also be repetitive for those not enticed by the challenge of perfecting each jump and mastering the levels.

8. What Other Games Have Been Developed by the Same Developer:
RobTop Games, the developer behind Geometry Dash SubZero, is well-known for the Geometry Dash franchise. Besides the games mentioned, they have also developed other titles including Geometry Dash Lite and the fully-fledged sequel, Geometry Dash 2.0, as well as a host of previous versions that laid the groundwork for the subsequent popularity of the series. The success of Geometry Dash has established RobTop Games as a respected developer within the rhythm-based platforming game genre.