1. **Introduction of the Game:**
Ultimate Custom Night (UCN) is a thrilling survival horror game that amalgamates characters from the iconic Five Nights at Freddy's (FNAF) series. Developed by Scott Cawthon, it serves as a customizable night where players can choose from an extensive roster of animatronics with varying levels of difficulty. The game's primary objective is to survive a night shift from 12 AM to 6 AM without being attacked by any of the malevolent animatronics.

2. **All Characters and Levels of the Game:**
UCN boasts an impressive and diverse lineup of over 50 animatronic characters drawn from the FNAF universe, each with customizability options in terms of AI difficulty levels, ranging from 0 to 20. Players can set the intensity for each character individually, leading to countless combinations and tailored playing experiences. The game itself is set in a singular, static level -- a security office where players remain stationary but must manage several defense mechanisms to fend off the encroaching animatronics.

3. **What Attracts Users Most to the Game:**
Players are predominantly drawn to UCN for its high-stakes strategy gameplay and the sheer variety it offers through extensive customization. The unique mix of tension, horror, and the ever-present threat of jump scares, combined with the deep knowledge required to effectively manage the horde of animatronics, keeps players continuously engaged. The fan service of integrating so many favorite characters into one game is an added bonus that nurtures a strong connection with the FNAF fanbase.

4. **Why It Is Popular:**
Ultimate Custom Night's popularity stems from its connection to the successful Five Nights at Freddy's series and the freedom it provides players to configure their nightmare scenario. The challenge of balancing numerous game mechanics at once - from camera systems to ventilation ducts, all while under pressure – creates an adrenaline-pumping gameplay experience. Additionally, the game's replayability, due to its varied difficulty settings and character combinations, continues to entice players.

5. **When the Game Was Released and How Many Versions Are Currently Available:**
Ultimate Custom Night was originally released on June 27, 2018, and as of my last update, that remains the main version of this specific title. While no subsequent versions of UCN have been released, the game has received updates to fine-tune its gameplay and mechanics.

6. **The Most Difficult Part of the Game:**
Many players consider the "50/20" mode to be the most challenging aspect of Ultimate Custom Night. This mode entails setting all 50 animatronics to their maximum difficulty level of 20. Completing this mode requires not only impeccable timing and quick reactions but also a deep understanding of each character's unique behavior and the strategy necessary to counter them.

7. **Strengths and Weaknesses of the Game:**
Strengths of UCN include its highly customizable gameplay, comprehensive roster of characters, and the challenge it poses to even the most skilled players. However, weaknesses could be observed in its steep learning curve and potential for overwhelming newcomers to the series. Some players might also find the lack of narrative progression or different levels to be limitations, as the game focuses intensely on repeating the core survival experience.

8. **What Other Games Have Been Developed by the Same Developer:**
Scott Cawthon is primarily known for the Five Nights at Freddy's series which includes multiple titles such as "Five Nights at Freddy's 1-4", "FNAF: Sister Location", "Freddy Fazbear's Pizzeria Simulator", and "FNAF: Help Wanted", among others. Outside of the FNAF franchise, Cawthon has developed several other games including "The Desolate Hope" and "Chipper & Sons Lumber Co." He has a reputation for creating engaging and unique gameplay experiences, primarily within the horror genre.