Expert Mode

Expert Mode is an unlockable gameplay mode in Shadow the Hedgehog where the player has to play through all of the game's stages in order to complete it. Expert Mode can only be unlocked in the game by attaining an A-rank on every single stage in the game.

Plot-wise, it is a form of training that Shadow apparently goes through shortly after the events of the game and is to be a true test of Shadow's skills.

Overview
In Expert Mode, the player plays through all 23 stages (including The Last Way) available in Shadow the Hedgehog in order, starting from the top of the level select chart down. Unlike the main game, progress will be lost if the player loses all lives or quits. Many of the first stages are nearly the same, just a few extra platforms and some more rings to use Light Speed Dash. No characters are allied alongside the player and there is no given rank after completing a stage. The objective of most stages is to reach the goal ring except for Central City (clear aninhiliator bombs), The Doom (rescue wounded researchers) and Mad Matrix (reach all four data-bases). The beginning of every stage has a hint marker containing a message from a different character wishing Shadow good luck and telling the player how Expert Mode works.

Stages Hint Characters
Every characters from the game including Cream the Rabbit and Cheese (even though they were only an objective in Cryptic Castle), Gerald Robotnik, the Commander, and even the President and his Secretary show up as hint characters. The final hint marker at the beginning of The Last Way gives luck from every single character seen in the game.
 * Sonic gives hints in Digital Circuit and G.U.N. Fortress.
 * Tails gives a hint in Glyphic Canyon.
 * Knuckles is featured as a hint character in Lethal Highway.
 * Rouge is featured as a hint character in Cryptic Castle and with Omega in Lava Shelter.
 * Omega is featured as a hint character in Mad Matrix and with Rouge in Lava Shelter.
 * Vector is the hint character in Prison Island and with other members of Team Chaotix in Final Haunt.
 * Charmy is the hint character in Sky Troops and with other members of Team Chaotix in Final Haunt.
 * Espio is the hint character in Central City and with other members of Team Chaotix in Final Haunt.
 * Amy is the hint character of Circus Park.
 * Cream is the hint character of The ARK while her chao is the hint character of Cosmic Fall.
 * Eggman gives hints in Westopolis and Iron Jungle.
 * Maria is featured as a hint character in The Doom.
 * Gerald Robotnik is featured as a hint character in Lost Impact.
 * The President and his secretary give hints in Air Fleet and Black Comet.
 * The GUN Commander gives hints in Space Gadget.
 * Black Doom gives hints in Death Ruins.

Trivia

 * The Expert Mode version of The Doom is the same as the Hero mission, except that the researchers are all next to a Heal Unit spawn in one room at the end.
 * Important and sometimes interesting information is often revealed by the hints at the start of each level in Expert Mode. Aside from the objective of each level, personal information from the speaker is sometimes revealed such as the Commander's new grandchild, the reason for the hostile actions of the Artificial Chaos, and the President's meetings.
 * In Mad Matrix, Omega claims that he is stronger than Shadow and challenges him. He wants to challenge Shadow again in Lava Shelter, but Rouge stops him.
 * In Iron Jungle, Dr. Eggman asks if Shadow is angry with him, which may refer to Shadow Androids.
 * The President tries to talk with Shadow in Air Fleet and Black Comet but in both cases his Secretary reminds him of his meetings and he has to stop talking with Shadow.
 * At the beginig of Final Haunt, Charmy and Vector fight with each other about minor matters and Espio apologizes to Shadow about it.
 * Cheese is the hint character of Cosmic Fall. However, Vector's voice can be heard in some parts of stage.
 * Gerald Robotnik says in Lost Impact that the reason the Artificial Chaos became hostile was because Gerald accidentally reversed the positive and negative electrode connectors within them. This created a problem in their programming and resulted in their hostility.
 * Sonic gives hints at the beginning of Digital Circuit.However; Rouge's voice is heard through the stage.