1. Introduction of the game:
Castle Crush is a fast-paced mobile strategy game where players collect and upgrade a variety of cards featuring spells, warriors, ancient beings, and fearsome creatures. With these cards, players engage in dynamic battles by deploying troops upon a two-lane battlefield, aiming to destroy their opponent's castle while defending their own. It's a game that fuses elements of collectible card strategy with exciting real-time combat mechanics, offering a unique gaming experience.

2. All characters and levels of the game:
Players in Castle Crush will discover a vast array of characters — from valiant knights and powerful wizards to dragons and other mythical creatures. Each character comes with its special abilities and strategic uses in battle. Additionally, the game features numerous levels, with players progressing through increasingly challenging ranks as they win battles, unlock new cards, and enhance their decks.

3. What attracts users most to the game:
The strategic depth combined with the excitement of real-time PvP battles is what hooks many players. The ease of learning the gameplay paired with the difficulty of mastering it provides a satisfying challenge. Moreover, the regular updates with new cards and events keep the game fresh and thrilling for ongoing entertainment.

4. Why it is popular:
Castle Crush has gained popularity due to its engaging gameplay, the satisfaction of collecting and leveling up cards, and the competitive atmosphere it fosters through player vs. player combat. It appeals to those who enjoy strategic planning as well as those who favor action-packed encounters.

5. When the game was released and how many versions are currently available:
Castle Crush was released on November 9, 2016. Since its launch, the game has been updated numerous times, with the developers releasing patches, fixes, and content updates to keep the game balanced and engaging. As for versions, there isn't a clear delineation since mobile games are often simply updated to the latest build rather than identified by version numbers.

6. The most difficult part of the game:
Many players find that as they reach higher levels, the game becomes significantly more challenging. The increase in difficulty could be due to facing more experienced opponents, encountering more complex card interactions, or the need for precise timing and strategy during battles.

7. Strengths and weaknesses of the game:
Strengths of Castle Crush include its addicting gameplay loop, the variety of cards and strategy available, and the active community. On the downside, like many free-to-play games, players may feel the progression becomes grindy or pay-to-win at higher levels, which can be a weakness leading to frustration among those who do not wish to make in-app purchases.

8. What other games have been developed by the same developer:
Castle Crush is developed by Fun Games For Free, a game development studio that has produced several mobile hits. Among their other popular titles are "Sniper 3D: Fun Free Online FPS Shooting Game," "War Machines: Tank Battle," "Colorfy: Adult Coloring Book - Free Style Color," and "Flight Pilot Simulator 3D Free." These games, like Castle Crush, focus on strong gameplay mechanics and accessibility to appeal to broad audiences.