1. Introduction of the game:
"Five Nights at Freddy's 4" is the fourth installment in the wildly popular and chilling horror game series created by Scott Cawthon. Released as a psychological horror game, it deviates from its predecessors by taking place in a suburban home where players must defend against nightmarish animatronics. Unlike previous games set in a security office, players assume the role of a child facing these creatures in their own bedroom, making the experience intensely personal and frightening.

2. All characters and levels of the game:
In FNaF 4, the characters are nightmarish versions of the beloved animatronics from previous games. These include Nightmare Freddy, Nightmare Bonnie, Nightmare Chica, Nightmare Foxy, and later in the game, Nightmare Fredbear and Nightmare. Unlike previous entries, the game progresses in nights, each increasing in difficulty, with a final night (Night 7) and an extra mode called "Nightmare" mode for an even greater challenge.

3. What attracts users most to the game:
The atmospheric tension and jump scares continue to be significant attractions in FNaF 4. However, the familiarity of "home" coupled with the distortion of childhood fears elevates the horror experience. Players are also drawn to the deep lore and story mysteries, compelling them to piece together the game's cryptic storyline and background.

4. Why it is popular:
The popularity of FNaF 4 lies in its successful formula of simplistic yet immersive gameplay and the use of psychological horror elements. The game's ability to place players directly into the shoes of a vulnerable child amplifies the fear and suspense. The growing fandom and the compelling need to resolve the series' lore also contribute significantly to its popularity.

5. When the game was released and how many versions are currently available:
"Five Nights at Freddy's 4" was initially released on July 23, 2015. The core game remains largely unchanged, but it has been regularly updated with patches and has an expansion called "Halloween Edition" with new characters and challenges.

6. The most difficult part of the game:
Many players find the latter nights of the game, including Night 7 and Nightmare mode, to be extremely difficult. The animatronics become more aggressive, and the game requires near-perfect timing and acute sound-based awareness to survive the night.

7. Strengths and weaknesses of the game:
Strengths include its intense atmosphere, compelling narrative, and unique take on the horror-genre gameplay. However, weaknesses may include a steep learning curve, the reliance on jump scares for shock value, and the potential for repetitive gameplay, which might not appeal to all gamers.

8. What other games have been developed by the same developer:
Scott Cawthon is the developer behind the entire "Five Nights at Freddy's" series, which includes the titles "Five Nights at Freddy's," "Five Nights at Freddy's 2," "Five Nights at Freddy's 3," "Five Nights at Freddy's: Sister Location," "Freddy Fazbear's Pizzeria Simulator," and several spin-offs and related games like "FNaF World" and "Ultimate Custom Night." He has also created other non-FNaF games earlier in his career, such as "The Desolate Hope" and "Chipper & Sons Lumber Co."