1. **Introduction of the Game:**
Red Ball 4 is a highly engaging physics-based platformer game where the heroic red ball embarks on a journey to stop nefarious squares from turning the planet into their square-shaped dystopia. With its simple yet captivating mechanics, players of all ages will traverse rolling hills, surmount obstacles, and solve puzzles using jump and roll controls.

2. **All characters and levels of the game:**
The game primarily revolves around the main protagonist - the Red Ball, who encounters various other characters such as black squares and bosses that attempt to impede its progress. The game boasts an array of exciting levels, spread across different episodes with increasing complexity and varied themes. Each new level brings fresh challenges and puzzles to solve, keeping the gameplay fresh and enticing.

3. **What attracts users most to the game:**
Users are most attracted to Red Ball 4 for its clean, colorful graphics, intuitive gameplay, and the pure satisfaction that comes from navigating the Red Ball successfully through the cleverly designed levels. The challenging physics puzzles also play a significant role in engaging the players deeply within the game's mechanics.

4. **Why it is popular:**
Red Ball 4's popularity can be attributed to its simple yet addictive gameplay that is easy to learn but hard to master. The game's charming character, accompanied by a whimsical musical score and progressively challenging levels, ensures a fun-filled experience for casual and seasoned gamers alike.

5. **When the game was released and how many versions are currently available:**
Red Ball 4 was released on July 17, 2014. Since its original release, the game has seen several updates and versions that expanded upon its original content with new levels and episodes, maintaining the interest of its user base. As for the specific versions and updates, they vary based on the platform (iOS, Android, etc.) on which the game is played.

6. **The most difficult part of the game:**
Many players consider the boss battles to be the most challenging aspect of Red Ball 4. These require not just quick reflexes but also a strategic approach to defeat each boss that has unique attack patterns and defenses.

7. **Strengths and weaknesses of the game:**
Strengths of Red Ball 4 include its simple yet engaging gameplay, delightful graphics, and the satisfying sense of progression through its levels. However, some may find the game relatively short, and its simplicity can be a weakness for those seeking more depth in their gaming experiences.

8. **What other games have been developed by the same developer:**
Red Ball 4 is developed by FDG Entertainment which has also produced other popular titles such as "Tentacle Wars," “Oceanhorn," "Banana Kong," and "Bloody Harry." These games also showcase FDG's signature polished graphics and engaging gameplay, catering to a broad audience of mobile game enthusiasts.