Red Mountain

Red Mountain (レッドマウンテン) is an action stage in Sonic Adventure and its remake, Sonic Adventure DX. It is a stage located on Angel Island in the Mystic Ruins adventure field and is a stage played by Sonic, Knuckles, and E-102 Gamma.

Overview
The entrance to the stage is guarded by a caged KiKi, which must be destroyed before it can be accessed (for Sonic, you must get the ancient light and do the "light speed attack" on it, for Knuckles, you must get the "monkey destruction switch" from a cave near the mystic ruins chao garden, and for E-101, you simple attack it like you attach any other enemy). The mountain appears to have been industrialized by Dr. Eggman, as the area is strewn with not only badniks, but crates, bridges, zip-lines, and construction equipment. This indicates that perhaps this is where Eggman harvest the resources to build his army. It's a very fast paced and tricky stage that can quickly lead to Sonic plummeting into the bottomless canyon if one isn't careful.

The second section of Red Mountain is located within the interior of a volcano. This area is filled with flowing lava, collapsing rocks, and dangerous enemies. A watchful eye is needed here, as the landscape of the level can change in seconds. If one pays attention to his surroundings, you can see that within the walls of the area, prison cells have been built. Inside, ghosts of doomed men sway to the beat of the heavy music that plays. There appears to be two electric chairs in both cells, and tombstones can be found nearby, suggesting that this was once some sort of prison.

Sonic
Sonic's version is the longest version of the stage. The first part takes place in the large mountainous region the stage gets its namesake from, and the second part dives into what appears to be an active volcano, before rocketing back up to the surface of the mountain. Right after Sonic finishes the stage, he spots Tails upgraded bi-plane; the Tornado 2, and he hops aboard to continue his chase after the Egg Carrier.

Knuckles
Knuckles travels here to find more of the missing Master Emerald shards. He only visits the first section of Red Mountain, never venturing into the volcano. Knuckles has a major advantage in this stage compared to Sonic, as his climbing and gliding abilities allow him to traverse the terrain much more easily.

E-102 Gamma
Gamma's mission in this stage is to "rescue" E-104 Epsilon. His is the shortest of the three characters that travel through it, his area of operation being a small section of the volcano. As with most of Gamma's stages, this Red Mountain is much more enemy heavy than either Sonic or Knuckles' versions.

Trivia

 * The music in the volcanic area is a remix of the theme "Crying World" from Ristar. The theme is played during the Planet Atomation stage.
 * Although he can't glide or climb like Knuckles, Sonic's Spin Dash, combined with the games questionable physics, allow him to take many major shortcuts by jumping over pits and lava. This is highly necessary in Sonic's A-rank mission, since the time limit is very tight.