Okay, I can create a 600-word text including game features, gameplay and other related content in the introduction of the game "Anonymous Letter: The Invisible" as required.

"Anonymous Letter: The Hidden Man" takes you through the Paris style of the early 20th century, a city full of art, romance and passion. In this dazzling golden age, an undercurrent is surging. Players will play the role of a legendary master of puppet art, explore the truth behind bizarre murder cases, collect hidden clues, unlock mechanism puzzles, and uncover the mystery of the evil hand.

Game features:

1. Visit the romantic Paris of the 20th century: The game carefully restores the style of Paris in the early 20th century, allowing players to immerse themselves in this era of art and passion.
2. Play as the legendary puppet master: Players will transform into puppet masters and use their wisdom and skills to reveal the truth and win honor for themselves.
3. Investigate the truth of bizarre murder cases: There are many bizarre murder cases in the game waiting for players to investigate. The truth is hidden among complex clues, testing the player's wisdom and carefulness.
4. Collect hidden clues and unlock mechanism puzzles: Players need to collect hidden clues in the game, solve puzzles and mechanisms one after another, and reveal the conspiracy and criminal truth hidden behind the scenes.
5. Obtain achievement rewards and collect exquisite wallpapers: There are multiple achievements in the game waiting for players to challenge. Completing the achievements can obtain rewards such as exquisite wallpapers, making the game more interesting and challenging.

How to play:

1. Players need to collect clues and evidence in the game, and uncover the truth of the case through comparative analysis and reasoning.
2. Explore corresponding levels and challenge dungeons based on scene clues and task prompts to collect case-related props and key information.
3. Communicate, cooperate, compete, and share experiences and skills with other players to solve puzzles and challenge more difficult tasks.
4. Players need to use their wisdom and skills to unlock puzzles and mechanisms, and reveal the conspiracy and criminal truth hidden behind the scenes.
5. There are also a number of achievements and challenge tasks in the game. Players can challenge themselves to gain a higher gaming experience and sense of accomplishment.

Player comments:

“Anonymous Letter: The Invisible is an engrossing game that combines mystery and puzzle elements to make you want to put it down.” — “This game is full of Surprises and suspense keep people guessing about the next development." - "The exquisite graphics and rich game content make you feel like you are in Paris in the early 20th century." - "As a puppet master, I deeply feel the game. Unique charm and challenge" - "Players who like puzzles and reasoning must not miss this game!"