1. **Introduction of the game:**
Hay Day is a delightful farming simulation game that invites players to step into the shoes of a farmer to grow crops, raise animals, and build a flourishing farmstead. Developed by Supercell, the game offers a charming rural setting, where players can experience the joys and challenges of farming life. With its vibrant graphics and engaging gameplay, Hay Day provides a relaxing and enjoyable environment for gamers of all ages.

2. **All characters and levels of the game:**
Hay Day doesn't have a traditional leveling system with characters, but rather a progression-based system where players unlock various farm animals, plants, and buildings as they gain experience points. Characters in the game include non-playable characters (NPCs) such as Greg, who is the player's neighbor and assists in introducing game mechanics. The player's levels progress by performing farm activities, leading to unlocking more sophisticated crops, animals, and farm equipment, enhancing both the capabilities and the visual appeal of their farm.

3. **What attracts users most to the game:**
Users are most attracted to Hay Day for its soothing gameplay that allows for creative expression in farm management. The game's social interaction elements, such as trading goods with friends and neighbors and visiting other farms, also contribute to its appeal. Additionally, Hay Day features seasonal events and updates that keep the content fresh and engaging.

4. **Why it is popular:**
Hay Day's popularity stems from its uncomplicated yet addictive gameplay, the satisfaction of watching your farm grow and evolve over time, and the ability to play at your own pace. Furthermore, the game's accessibility to a wide audience and its cartoonish, friendly aesthetic have made it a favorite among casual gamers.

5. **The most difficult part of the game:**
For many players, the most challenging aspect of Hay Day is effectively managing the game's economy. This includes balancing the demands of crop growing, animal rearing, and product manufacturing with limited resources like space, time, and in-game currency. Additionally, mastering the art of timing and trading in the global marketplace for optimal profit can be a significant challenge.

6. **Strengths and weaknesses of the game:**
Strengths of Hay Day include its engaging farm simulation gameplay, the vast variety of tasks and activities, and the frequent updates that provide fresh content. Weaknesses could be seen in the pace of the game, which might be slow for players looking for more action, and the dependency on in-app purchases for faster progression, which could be seen as a barrier for some.

7. **What other games have been developed by the same developer:**
Supercell, the developer behind Hay Day, is known for several other highly successful mobile games, including Clash of Clans, Clash Royale, Brawl Stars, and Boom Beach. Much like Hay Day, these games feature Supercell's signature blend of engaging gameplay, social interaction, and regular content updates.