Summoners War: Sky Arena is a captivating mobile turn-based strategy massively multiplayer online game (MMO) that combines collecting monsters with intense RPG elements. Developed and published by Com2uS, the game transports players to the mystical Sky Arena where they assume the role of a Summoner. These Summoners wield the power to call forth powerful creatures and beasts to fight in tactical battles for control of the vital resource known as Mana Crystals.

All characters and levels of the game:
Summoners War boasts an expansive roster with over 1,000 different monsters to collect, each with unique abilities, five different attribute alignments (Water, Fire, Wind, Light, and Dark), and various star ratings that signify their potential power. The monsters range from one to six stars, with six-star creatures being the most powerful. Levels in the game encompass multiple scenarios with increasing difficulty, a tower of ascending challenges known as the Trial of Ascension, dungeon explorations for runes and monster materials, and special themed events.

What attracts users most to the game:
Players are most attracted to Summoners War by the depth of strategy involved in assembling and empowering a team of monsters. The game’s engrossing progression system, the thrill of summoning rare monsters, and the competitive aspects, such as the PvP Arena and Guild Wars, keep players engaged. Additionally, the frequent updates, special in-game events, and a supportive community add to its appeal.

Why it is popular:
Summoners War's popularity lies in its complex yet accessible gameplay, the rewarding loop of collecting and upgrading a vast array of monsters, and the sheer variety of content it offers. Its stunning graphics, engaging storyline, and the social elements of joining guilds and battling other summoners contribute to its wide-reaching appeal.

When the game was released and how many versions are currently available:
Summoners War was released on June 12, 2014. While the game itself has not been released in multiple versions akin to some other games, it has been regularly updated with new content, features, and quality-of-life improvements over the years. These updates are considered different versions or patches, though the core game remains as a single, evolving title.

The most difficult part of the game:
The most challenging aspect of Summoners War can vary by player, but many agree that achieving high ranks in the competitive PvP Arena, conquering the latter floors of the Trial of Ascension, and clearing the highest-level dungeons for top-tier runes pose significant challenges. These end-game activities require not only powerful and well-equipped monsters but also thoughtful strategy and team composition.

Strengths and weaknesses of the game:
Summoners War's strengths include its diverse and extensive collection of monsters, engaging strategic gameplay, and active community. However, its weakness might be seen in the grind-heavy nature of the game that can require considerable time investment to progress, especially at higher levels. Additionally, the game's reliance on in-app purchases can be seen as a pay-to-win aspect by some players.

What other games have been developed by the same developer:
Com2uS, the developer behind Summoners War, has also developed several other popular mobile games, including "Hive," a gaming platform that hosts a variety of games and social features, "Soccer Spirits," a card-based soccer simulation game, and "Skylanders: Ring of Heroes," another role-playing game similar to Summoners War with a focus on characters from the Skylanders universe.