X-mode (X-Ray mode) is one of the three X-Ray Scope glitched modes, the other two being R-Mode and G-Mode. This is the mode enabling Superjumps. Thus, it is the most useful for TAS, but RTA applications tend to be few and far between.
X-mode requires the fewest items, only requiring X-Ray Scope. However, most set-ups require additional items. The easiest set-up requires Morphing Ball. The set-up that allows its usage seemingly anywhere in TASes requires Ice Beam.
In current routes of categories, X-mode has very few applications. There is Jesuswalk, used in 14% xAmmo (and an option in other 14% categories, although usually more difficult than a different choice). Additionally Max% GT Code has a route that crosses Bowling Alley by using Spike X-mode.
X-mode may be used to generate a blue suit which has uses in 14% categories.
Other than these, most applications of X-mode to speedruns are theoretical, via use of Superjumps. Perhaps the most famous is GT Superjump.
The below is some base information, that should be further fleshed out.
X-mode is entered by frame perfectly using X-Ray the frame before knockback ends. This cannot normally be done, so there are different set-ups to make it possible.
The easiest method is Spike X-Mode. This requires Morphing Ball. To perform: Bounce in Morph near spikes so that you will land on them, select X-Ray and hold dash, hold forward before the spikes damage Samus, and unmorph frame perfectly.
Therefore, this is easiest because the dash input for activating X-Ray is buffered due to the unmorph animation.
To tell if you got the correct frame, here is what happens at various unmorph frames:
- More than 8 frames early: X-Ray is used before knockback occurs.
- 2-8 frames early: Knockback occurs after the unmorph so X-Ray fails.
- 1 frame early: The unmorph fails.
- Correct frame: X-mode is entered, see below
- 1 frame late: X-Ray is used while standing.
- 2 or more frames late: Knockback occurs before the unmorph.
- 2 frames late: X-Ray is used while crouched.
- 3 or more frames late: Samus will be in the air so X-Ray will fail.
If done correctly, Samus' legs will be moving as if she were running and X-Ray will be active, but Samus will not be moving.
This can also be done by hitting spikes twice in a row. This requires having more health, but may be easier to learn. The first spike hit is used to bounce in morph form, and then the unmorph happens frame perfectly just before the second spike hit.
Rather than bouncing in morph, you can instead bonk into the side of something (such as a platform or a frozen enemy) prior to landing on the spikes. Below are examples of the 3 methods described above.
Similar to a slopespark, a slope may be used to land before knockback frames are over. This allows using X-Mode.
It appears that in order to do this, a frame perfect switch from holding forwards to holding backwards may be required, to get downwards knockback and land as soon as possible. Thus this has questionable RTA viability, but this requires further testing.
This is a variant of Slope X-Mode: While doors are closing, they act like slopes.
This is done by taking damage while going through a transition (while facing away from the transition), similar to getting door stuck for an X-Ray Climb.
Like Slope X-Mode, many of these set-ups seem to require a frame perfect switch from forwards to backwards. There is at least an exception for Jesuswalk on PAL.
Frozen Enemy X-Mode
Using a frozen enemy, Samus may land very quickly. This is what TAS does to do Superjumps basically anywhere.
This method would not be very RTA viable, since it may require pixel perfect enemy and Samus positioning and hence many frame perfect inputs. For any particular application, a set-up could possibly be found. It would still be very inconsistent.
The reserve tank automatic refill can extend the knockback timer. This can be used to allow entering X-Mode where it would otherwise be impossible.
The most famous example here is GT Superjump.
X-Mode is exited by stopping the use of X-Ray.
Samus will appear to be moving forward. In some instances of X-Mode, Samus will automatically move forward (TODO: When does this happen?). In most instances, Samus will only actually move forward by arm pumping. Samus will move straight forward, without falling, walking on air.
Touching a wall will crash the game.
Crouching in X-Mode will cause Samus to crouch and be unable to move until X-Mode is canceled.
Jumping while in X-Mode will cause Samus to be in a jumping state. Just as she does not move forwards, she will not actually move. If X-Mode is released, she will gain that momentum. This is useful for getting off of the spikes when Spike X-Mode is used.
If X-Mode is entered with non-zero dash speed, a shinespark may be charged. Since Samus is (most likely) not moving, this allows charging a shinespark in a very short distance.
X-Mode may be entered with a shinespark suit, despite the use of X-Ray. Note if the method of entering X-Mode requires a damage boost, this may not be possible since the damage boost may use the spark.
If Samus shinesparks while in X-Mode, every frame her vertical momentum is increased by 7 pixels. Since she is in X-Mode, this momentum is not actually applied until X-Mode is canceled. Then it is immediately applied, she loses horizontal momentum, and she is put in a falling state.
This allows gaining absurd amounts of speed, and will frequently cause Samus to go flying Out of Bounds. The precision in placement and X-Ray release needed for applications makes this extremely difficult to be useful RTA.
Current routes of categories use X-Mode infrequently.
X-Mode is a fairly simple method of generating a blue suit, especially the spike method. It can frequently be the fastest choice. For example, in 14% xSpeed before entering Maridia it should be fastest to get a blue suit in Hellway via X-Mode.
To generate a blue suit with X-Mode, simply shinespark while in X-Mode and cancel it before the crash.
Given the tendency of Superjumps to go Out of Bounds, it is safest to cancel X-Mode during the windup for the shinespark. Note that if a Spike X-Mode is used, this means that Samus will be on spikes and will now have a blue suit. Thus, damage can be taken very quickly.
To do this, bounce on the ledge and then X-Mode on the spikes. Samus will appear to be running in place. Release forward, and Samus will move slowly across the room. The Chozo will eventually come into sight. When you think you are close enough, press jump, then release dash to exit X-Mode. If you do this too late, you will run into the wall and the game will crash. If you are worried that you'll go too far, you can hold forward to stop Samus from moving, then arm pump to move her closer to the Chozo pixel-by-pixel.
Crossing Colosseum suitless without Space Jump, Grapple, or Ice Beam can be quite tricky. This is especially true going from right to left, where the last jump from the spike is extremely precise.
Instead, a short Spike X-Mode can be used to make this jump easier. This isn't too terrible, despite being frame perfect, due to the nearby Save Room.
There is a relatively simple set-up, by taking damage from a crab during the transition while low in the door in a spinjump. This allows buffering all of the inputs (backwards, jump, angle, and dash). Then the trick reduces to releasing backwards and jump frame perfectly.
There is a method to cross Mt. Everest with a Superjump using via a door X-Mode. It is claimed this only works on PAL, and the only clip of it requires a frame perfect switch from left to right to get a downwards knockback. If this method is humanly feasible, it would allow 14% xSpeed to be completed without the use of L+R wall jumping. However, the segment containing this trick would be extremely difficult, requiring: G-moding into Maridia, managing to get a shinespark suit afterwards, performing this Jesuswalk Superjump, continuing with the blue suit while fighting Botwoon, sparking up Halfie Climb Room, and then traversing Colosseum with minimal equipment before being able to save.
This is a well known application from the 100% TAS. It uses a reserve tank extended knockback to get X-Mode in Golden Torizo's Room, to collect GT Missiles without Space Jump by using a Superjump.
This would enable a single Norfair route of 100%.
Not only is this method incredibly precise and thus fairly infeasible, it is also believed to not be faster for RTA 100%. Getting through Lower Norfair with this equipment is significantly slower, thus losing all of the gained time.
Here, other uses (including theoretical applications to categories) can be documented as they come up.