1. Introduction of the game:
Pou is an endearing and highly engaging mobile game that revolves around the concept of virtual pet care. In this game, players are tasked with the responsibility of raising and taking care of a cute, alien-like pet named Pou. This involves feeding it, cleaning it, and engaging with it through various mini-games and activities, ensuring its well-being and happiness.

2. All characters and levels of the game:
While the central character of the game is Pou itself, players can personalize their virtual pet with different outfits and accessories to make it unique. As for levels, the game doesn’t follow a traditional level structure. Instead, the game progresses as Pou grows, with new mini-games and items unlocked as the player's virtual pet evolves and ages.

3. What attracts users most to the game:
Players are most attracted to the emotional attachment that forms with their virtual pet, Pou. The customization options for Pou, alongside the array of mini-games that are not only entertaining but also addictive, keep players engaged. The simplicity and charm of nurturing a virtual life form also play a significant role in the game’s allure.

4. Why it is popular:
Pou gained popularity due to its unique take on the virtual pet genre, appealing to a broad demographic that includes both children and adults. Its ease of play, coupled with the emotional bond that develops between players and their pet, has led to its enduring popularity. Additionally, the constant updates and new features introduced keep the game fresh and exciting.

5. When the game was released and how many versions are currently available:
Pou was released on August 5, 2012. Since its initial launch, the game has seen numerous updates which have improved upon the original version. These updates have brought new features, mini-games, and customizations, although they do not constitute separate versions of the game. It has been widely distributed on multiple mobile platforms with regular maintenance updates.

6. The most difficult part of the game:
Arguably, one of the most challenging aspects of Pou is ensuring the constant attention and care for the pet. While the game is not difficult in the traditional sense, the mini-games do offer varying levels of challenge, and some require a fair amount of skill and dedication to master.

7. Strengths and weaknesses of the game:
Among its strengths, Pou boasts a user-friendly interface, engaging mini-games, and the joy of pet customization. The game's simple yet captivating gameplay loop is highly accessible and can cater to quick gaming sessions. On the downside, as with many virtual pet games, the repetitive nature of tasks and the need for frequent engagement might not appeal to everyone. Also, as the game relies on in-app purchases for certain customizations and power-ups, players who do not wish to spend real money might find progression slower.