Screw Attack is an item in Metroid Prime 2: Echoes and Metroid Prime 3: Corruption. Its appearance in Echoes is the first appearance of Screw Attack in a 3D Metroid game and it allows Samus to cross large horizontal gaps using up to five individual Screw Attacks at a time. It also has damaging properties, with many enemies and even certain bosses in Echoes being vulnerable to the attack.
In Metroid Prime 2: Echoes, Screw Attack is a required item for beating the game due to the Screw Attack Walls that are needed to climb the room Sanctum Access.
Mechanically, Screw Attack in the Prime games is less versatile than in its 2D counterparts, at the tradeoff of it being more powerful. In order to activate Screw Attack, the following conditions have to be met:
- The player needs to have pressed B at least 2 times, and on the third B press:
- Be in the air
- Be looking horizontally (i.e. not upwards or downwards)
- Be moving forward
- If currently using the Charge Beam, the number of required B presses increases to 5 times, which is useful in wallcrawls
Once in Screw Attack, the player has limited control over Samus wherein turning the analog stick right or left will move Samus towards that direction when doing one of the Screw Attacks. The player has an upward of five uses of Screw Attacks, after which Samus is forced to fall. The quicker a Screw Attack is performed, the less distance she moves overall, at the tradeoff of having more speed. The slower a Screw Attack is performed, the more horizontal distance is crossed, at the tradeoff of having lesser speed. Thus, optimal Screw Attack movement depends on the tradeoff between how much distance you cross and how fast you're going while in the Screw Attack sequence. Additionally, damage taken from Dark Aether's atmosphere is reduced while in Screw Attack.
At the end of the Screw Attack sequence, Samus will fall. This happens if the player presses B too quickly, has exhausted all five of their jumps, or bonks on a wall. It is important to note that Samus will not transition out of the Screw Attack sequence until she lands on a standable spot. If Samus never lands on a standable spot, the game will be effectively softlocked, forcing the player to reset. This means that if Samus falls and is out of bounds, she can easily fall below the bottom of the room and keep falling indefinitely. The same effect can also occur if Samus lands on a piece of collision out of bounds that is not standable.
Screw Attack does 36 damage per frame in Metroid Prime 2: Echoes. Certain bosses, including every Dark Samus fight and the first and third phases of Emperor Ing are vulnerable to Screw Attack, leading to major timesaves in speedruns. Certain objects can also be damaged or destroyed with Screw Attack that aren't obvious, such as the light crystal in Crypt, the crystal-activated door in Main Reactor, as well as the rubble in Main Gyro Chamber. It can also be used to destroy every seeker door in Metroid Prime 2, leading to development of seeker skip.
In the original release of Metroid Prime 2: Echoes, the hitbox that the game uses for Screw Attack is the same as the hitbox of the Morph Ball. Consequently, this means that in any Morph Ball tunnel that Samus can fit through, she will be able to go out of bounds once the game goes back into first person mode and changes her hitbox. This can also be done in certain tight spaces, such as the one in Dynamo Works. This was patched in the Trilogy release of the game.
Screw Attack Unmorph
When Samus finishes the Screw Attack sequence, she will "unmorph" back into first-person, similarly to what happens when Samus is unmorphing from Morph Ball. The unmorph sequence has some properties that can affect movement.
Screw Attack bugs when Samus enters the Screw Attack sequence directly after an Instant Unmorph. Instead of showing the normal animation, Samus will instead have a glitched animation and will not be spinning while in the sequence. As a result, Samus will take longer to transition out of Screw Attack when the sequence is over.
Instant SA Unmorph
If Samus gets the above glitched animation, then she can unmorph from Screw Attack early, without needing to touch the ground. This can happen when the first B press after the Instant Unmorph occurs while Samus is in Jumpstate 2.
This can also happen when Samus bonks onto a wall, provided that wall is within a short distance of Samus.
For a TAS, this invites the possibility of using SA as the final part of a complex bomb jump sequence in order to gain a lot of height. See, for example, this video where this is applied on Crossroads as an alternative method to the existing SW.
Screw Attack Without Space Jump
The behavior of Screw Attack changes when Samus doesn't have the Space Jump Boots. Because the game doesn't expect you to get Screw Attack without Space Jump, its mechanics are far more difficult to utilize.
The Z-Axis is a variable that the game uses to determine the range at which Samus can perform one of the five Screw Attacks. Note that this is not to be confused with Samus' own Z-Axis, which is independent of the Z-Axis that Screw Attack uses to function. When one of the game's regions is loaded, this value is set to zero. Normally, the Z-Axis automatically updates whenever Samus performs a Space Jump, but if playing NSJ, this value cannot be updated by the player. If Samus is too far below the Z-Axis, she will almost immediately cancel her Screw Attack before the player has the chance to perform a Screw Attack at all. The behavior is slightly different if she is above the Z-Axis, in which case she won't be able to perform a Screw Attack, but the Screw Attack sequence won't be immediately cancelled.
Screw Attack Walls can be used to update the Z-Axis even without Space Jump. It's easier to update the Z-axis to a higher value since Samus doesn't immediately cancel Screw Attack at higher values, but updating it to a lower value is also possible. This is used in Sanctum Access in order to climb the room without Space Jump, as the Z-axis in the Sky Temple is below the map by default.
If Samus enters a Terminal Fall trigger, then performs a Screw Attack on the frame before her position gets changed, Samus will have a glitched HUD. The HUD is the same as the HUD that displays while in Morph Ball, but it will look incorrect because it is displaying in first-person. The HUD will return to normal if Samus performs another Screw Attack or if she takes an elevator. The only known behavioral difference of this HUD is that switching to Dark Visor will crash the game.
TODO: Add image or video demonstrating the glitched HUD