Grind Rail

Grind Rails, also known as rails, are recurring elements in the Sonic the Hedgehog series. They allow characters with the ability to grind to jump on rails 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 (Battle) was the first Sonic game to feature grinding. Only Sonic the Hedgehog and Shadow the Hedgehog can grind in this game. Grinding is relatively difficult due to the fact that the grind rails are extremely thin, and cannot be targeted with a Homing Attack like in later games. Also, the player must actively tilt the control stick to balance on the grind rail, or else the character will slow down and eventually fall off. Pressing and holding the action button will cause Sonic or Shadow to crouch and thus gain speed. Grind rail switching is performed by holding the control stick in the desired direction and pressing the jump button.

Strangely, at least in the Dreamcast version of the game, an invisible grind rail is present in Knuckles' level, Meteor Herd. As Knuckles can't grind, it can only be utilized by hacking Sonic or Shadow into the level. It doesn't actually lead anywhere specific, so it is likely a beta remnant.

Sonic Advance
In the GBA game Sonic Advance, grinding can only be performed by Sonic and, oddly, Amy Rose. It can only be performed in a few acts including Neo Green Hill Zone Act 1. It is an obscure move that is never required to progress in the game, the player must jump at the flat portion of the grind rail at the top, and press the R button. Sonic and Amy will slide down the grind 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 grind rail will result in grinding, and also an integral part of the level designs. Jumping while on a grind 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. This style of acceleration was favored for future games. It is possible to travel up a vertical grind rail with no momentum by rapidly pressing the action button. Also, in this game, balancing manually is not required, though it is possible. 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. 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 grind rails to move faster.

Shadow the Hedgehog
Shadow the Hedgehog allows Shadow to grind in its stages. This is the first game where balancing cannot be executed at all. Pressing the secondary action button (the same button that performs the Ring Dash and Spin Dash) will cause Shadow to perform a Heroes-style rail trick, which curiously bounces him high enough off the grind rail to miss rings. Shadow can use weapons on grind rails.

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

Sonic Rivals and Sonic Rivals 2
Grinding can be performed by all characters. The player can jump off by pressing the Jump button while holding down.

Sonic and the Secret Rings
Sonic can again grind by jumping on rails. Tricks can be performed by pressing the Jump button, while rail switching requires the player to quickly tilt the Wii Remote to the appropriate side. Sonic can halt while on a rail, causing him to fall off. Some rails are invisible and only appear when Sonic lands on them.

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, unfortunately, creates conflicts with whether the character will jump off the grind rail or perform a trick.

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

Sonic Unleashed
In Sonic Unleashed, grinding works just as in previous 3D installments. Rail boosters were introduced that would give the player an extra boost of speed on a grind rail just like a dash panel. Grind rail switching (only in the Xbox 360/PS3 versions of the game, and dark gaia stage in Wii/PS2 versions.) is 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.

The beginning of a grind can contribute to an active Action Chain (Wii/PS2 version only). It cannot start one.

Sonic and the Black Knight
Sonic can grind on grind rails, though they rarely occur in the levels themselves. Usually Sonic will use a ballista to launch a grappling rope to a wall, and then grind on the rope. On the grind rails, the tricks from the previous 3D games can be performed, and Sonic can swing his sword. On the ropes, Sonic can jump higher than usual.

Sonic Colors
In Sonic Colors (Nintendo Wii), grinding is the same as in Unleashed, with the addition of a "Grind Bonus" that awards 3000 points periodically for grinding, and the player can switch grind rails using the analog stick.

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 grind rails do not permit the player to boost once on them, notably in Green Hill. A certain grind rail in a stage also simply requires Sonic to jump to switch to another grind rail. Classic Sonic can also grind in certain stages like City Escape, but instead of standing, he rolls down the grind rails.

In the Nintendo 3DS version, grinding is the same as in the Nintendo DS games. However, due to the 3D nature of grind rails in the game, the physics are slightly changed. When Sonic jumps, he lands back on the grind rail, but he can fall through the grind rail if the player holds the down button and jumps. Classic Sonic's stages do not feature grind rails in this game. Mushroom Hill's 3D segment at the end involves Sonic boosting along a grind rail with the camera in a fully behind-the-back view. Tropical Resort also features the second grind rail-switching section in a portable game, where Sonic jumps from rail to rail to dodge falling meteorites; here he cannot boost.

Trivia

 * In Sonic Adventure 2, Sonic and Shadow are shown to possess 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.
 * In Sonic Unleashed, Sonic Colors and Sonic Generations, when there are two or more grind rails next to each other, switching from rail to rail seems to increase speed, likely by reducing friction.
 * Later games let Sonic start grinding at a fixed speed (this means that even if Sonic were walking up to a grind rail, touching it would cause him to grind quickly). In Sonic Adventure 2 and Sonic Heroes, this is not the case, as Sonic's current momentum carries into the grind.
 * The level Rail Canyon from Sonic Heroes has more grind rails than any other stage in the entire game series.