Grind Rail

Rails, also known as Grindrails, are a recurring element in the Sonic series. They allow characters with the ability to grind to jump on the rail and slide down it to reach new areas. The characters who can grind have varied from game to game.

Sonic Adventure 2
Sonic Adventure 2 (Dreamcast, Gamecube) was the first Sonic game to feature grinding. Only Sonic and Shadow can grind in this game. Grinding is relatively difficult due to the fact that the rails are extremely thin, and cannot be targeted with a homing attack. Also, the player must actively tilt the control stick to balance on the rail, or else the character will slow down and eventually fall off. Pressing B will cause Sonic or Shadow to crouch and thus gain speed. Rail switching is performed by holding the control stick in the desired direction and pressing the jump button.

Sonic Advance
In the GBA game Sonic Advance, grinding can only be performed by Sonic and, oddly, Amy. It can only be performed in a select few acts including Neo Green Hill Zone Act 1. It is an obscure move that is never required to progress in the game, and is quite a hassle to use: the player must jump at the flat portion of the rail at the top, and press the R button. Sonic and Amy will slide down the rail and be launched off into the air at the end.

Sonic Advance 2 and Sonic Advance 3
All playable characters in these games can grind, marking the first time that Tails, Knuckles, and Cream have been shown to possess this ability. It is now automatic, meaning that simply jumping at the rail will result in grinding, and also an integral part of the level designs. Jumping while on a rail will cause the player to jump off.

Sonic Heroes
In Sonic Heroes, all 12 playable characters across all 4 teams can grind. Unlike in Sonic Adventure 2, crouching is not utilized; instead, pressing the action button will cause the lead character to perform a small trick that accelerates their speed, regardless of momentum. It is possible to travel up a vertical rail with no momentum by rapidly pressing the action button. When in flight formation, grinding is much slower, and it is not possible to perform tricks.

Sonic Rush
In the Nintendo DS game Sonic Rush, grinding works the same way as it did in the Advance series; Blaze is revealed to possess the ability to grind. Rail tricks from Sonic Heroes returned, but they work differently: to perform a rail trick, the player must press the R button, which then gives Sonic or Blaze both a score bonus (up to 1700) and a small amount of boost energy. Closer inspection reveals that this version of the tricks also increases speed if there is no current momentum. Sonic and Blaze can both boost on rails to move faster.

Sonic the Hedgehog (2006)
Grinding works the same way as in Sonic Heroes, with the same style of rail tricks returning. This is the first time that rails can be targeted with a homing attack. All playable characters can grind.

Sonic Rush Adventure
Grinding in this game works the same way as it did in Sonic Rush; however, rail tricks can now be performed by pressing the A or B buttons as well as the R button. This, however, creates conflicts with whether the character will jump off the rail or perform a trick.

Plant Kingdom Act 1 features a 3D rail-switching section, a first for a handheld game.

Sonic Unleashed
In Sonic Unleashed, grinding works just as in previous 3D installments, but this time, the player doesn't need to manually balance on the rails. Rail boosters were introduced that would give the player an extra boost of speed on a rail. Rail switching was now performed using the trigger buttons, instead of using the control stick and the jump button. The tricks from Sonic Heroes and Sonic the Hedgehog (2006) can be performed.

Sonic Colors
In Sonic Colors (Wii), grinding is the same as in Unleashed, with the addition of a "Grind Bonus" that awards points periodically for grinding.

In the DS version, grinding is the same as in Rush/Rush Adventure, but without the trick system.

Sonic Generations
In Sonic Generations (console), grinding is the same as in Unleashed and Colors. Interestingly, certain rails do not permit the player to boost once on them, notably in Green Hill. A certain rail in said stage also simply requires Sonic to jump to switch to another rail. In the chase section for Green Hill, Sonic grinds away from a giant Chopper that attempts to destroy the rail and eat Sonic. Classic Sonic can also grind in certain stages like City Escape, but instead of standing, he rolls down the rails.

In the Nintendo 3DS version, grinding is the same as in the Nintendo DS games. However, due to the 3D nature of rails in the game, the physics are slighty changed. Tropical Resort also features the second rail-switching section in a portable game, where Sonic jumps from rail to rail to dodge falling meteorites.

Trivia

 * In Sonic Adventure 2, Sonic and Shadow are shown to posess Soap grinding shoes, as part of a promotional for the shoe company. Later games dropped this, and allowed Sonic to simply grind with his regular shoes.