Boost Ball
Boost Ball is an item in the Prime games that upgrades the Morph Ball, allowing it to boost while on land, giving Samus a lot of speed in return. It is used in a variety of different ways, from its intended use of moving up half-pipes, to general movement optimization, to activating designated morph ball spinners. It is even the basis for many different tricks and individual room strategies.
General
The behavior of the Boost Ball differs between games, leading to large differences for how it is used in speedruns. Despite this, there are a few tricks that persist between games.
Sideways Unmorph
Using light analog inputs, it is possible to get Samus moving in one direction, boost in that direction, and then have Samus be facing in a different direction when she is unmorphing. This is because the game updates Samus' facing angle to the direction she is rolling in when the player uses stronger analog inputs (i.e. when the analog stick is fully pointing in one direction.)
Wall Boosting
A wall boost occurs when the Boost Ball is used on a wall while the Morph Ball is moving upwards as a result of colliding with it. This is mainly used to save time in certain Morph Ball tunnels without needing to wait for a bomb to raise Samus.
Metroid Prime
In Prime 1, the Boost Ball can be found in the room Phendrana Canyon. The Boost Ball in Prime 1 has no speed cap, and additionally, there is very little delay that is added between boosts, meaning that it is possible to gain large amounts of speed very quickly.
Infinite Boosting
Infinite Boosting is a trick that's exclusive to Prime 1, since it's possible to boost so quickly. It's done by going out of bounds and boosting into any piece of collision. The Morph Ball will stick to the collision, allowing Samus to boost for indefinite amounts of time. When Samus unmorphs, she will be placed inside the room, provided enough speed has been built.
It can also be done inbounds in certain circumstances, such as bypassing the laser wall in Elite Research from behind.
Metroid Prime 2: Echoes
When the game starts, Samus will already have Boost Ball in her inventory, and this can be kept using Item Loss Skip. If the player goes through the item loss sequence however, Boost Ball can be obtained by fighting Boost Guardian in Dark Torvus Arena. The Boost Ball has a greater delay between boosts in Echoes (about a second), making infinite boosting impossible and reducing its overall speed benefits.
Boost Cooldown
After performing a Boost, the game starts a short timer lasting approximately a second. This timer restricts Samus from boosting until it returns back to 0. Due to the way this timer is programmed, it has a number of small quirks. Namely, if Samus performs a Boost and unmorphs immediately afterwards, then the timer will be stuck until Samus morphs again. This means that the next time Samus morphs, it will take longer than normal for Boost Ball to start charging again, because the cooldown period still won't have ended by that point.
Boosting Through Walls
While infinite boosting is impossible to do in Echoes, it is still possible to boost through walls while unmorphing sideways. This can also be done in Prime 1 to reduce the time spent on infinite boosting, though it isn't required there.
Sticky Boost
Sticky Boosts are a trick that was introduced in Echoes. It requires that the player be attached to a Spider Ball track and be hanging off the very edge of it. By boosting, Samus will be propelled in that direction. This is mainly used during the Power Bomb Guardian boss fight.
Metroid Prime 3: Corruption
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