For speedrun purposes, R-mode mostly finds use in low% categories, a small exception being a route of Super Metroid Z-Factor 100%. It can be used in 14% xChargeless, 14% xSpeed, 14% xAmmo, and the theoretical 14% xPb. It could also be helpful in low% versions of other categories, like low% RBO or low% Map Completion.
R-mode is activated by entering a transition, having Samus' Energy deplete to 0 during the transition, and then using X-Ray on the first frame after the transition while Reserves automatically trigger. This leads to the following steps:
1) Have Reserves set to automatic, X-Ray selected, an enemy positioned so it will hit Samus during the transition, and a small enough amount of Energy such that the enemy will damage Samus down to 0 Energy.
2) Enter the transition while in a pose that X-Ray can be used.
3) Be hit by the enemy during the transition.
4) Hold dash during the transition, so X-Ray is used on the first frame.
5) Continue to hold dash until Reserves have been emptied.
If dash is released very early, nothing notable will happen. If dash is released in about a three frame window when Reserves finish filling, then instead G-mode will be activated. Thus, it is safer to hold X-Ray for longer. Note X-Ray will do the widening animation again when Reserves finish filling, so when this begins for the second time dash can be released.
Based off the above description, it is fastest the enter R-mode with a very small amount of Energy in Reserves. However, many applications require getting Energy back into Reserves. Thus, it is usually more optimal to perform R-mode when Reserves are full.
The screen will be dimmed (like X-Ray is being used), and the door will close behind Samus. If the screen is not dimmed, then dash was released very early. If the door does not close, than X-Ray was released slightly too early and G-mode was activated instead.
There may be some graphical glitches, especially if power bombs are used. These will be more common if the room is larger. The pause screen will be a bit messed up, but is fully functional.
If a Crystal Flash is performed, the small light orb will follow Samus around and there may be further graphical glitches. Additionally, where the power bomb for the Crystal Flash was placed will continue to damage enemies.
The most important effect of R-mode is that the first time Reserves are automatically triggered, Samus is put into a standing pose (and R-mode is canceled). This includes if Samus is morphed (but excludes if Samus is in a forced crouch pose). This is frequently called an R-mode forced stand.
R-mode is canceled when Reserves automatically trigger, X-Ray is used, or a different room is entered.
The most evident limitation is the enemy positioning needed to enter R-mode. Note that the damage taken must be from an enemy. Projectiles will not work (they do not move during transitions, so will always damage Samus before the transition is triggered). Additionally environmental damage (e.g., heat) will not work. Therefore, a neighboring room needs an enemy that can damage Samus during the transition.
Most applications of R-mode use the forced stand. This requires having Energy in Reserves. Therefore, this requires either: (1) Crystal Flashing; (2) an infinitely respawning enemy; or (3) having more Reserve Tanks than Energy Tanks, performing R-mode when Reserves are full, and collecting a single health drop to put Energy in Reserves.
Note for (3), this could, in principle, be done with fewer relative Reserve Tanks if there are enough enemies in the room. This is usually not practical.
Another limitation is that R-mode requires using X-Ray, so activation will cancel a shinespark suit. R-mode can be activated with a blue suit, although requires a 1 frame movement (i.e., Samus must be one pixel away from the transition tile).
Also, a small note, an R-mode forced stand will not happen from a forced crouch, the pose Samus is in when she jumps into a 2-tile tall area and cannot use X-Ray. It will work from a normal crouch, and seemingly any other situation.
Finally, R-mode requires triggering a transition while in a pose that X-Ray can be used. This isn't a problem for horizontal transitions, where Samus can simply walk into the transition. For vertical transitions, this an issue.
For an upward transition, an appropriately frozen enemy (or some other enemy that Samus can stand on, e.g., a Yard) can be used. The enemy should be frozen at a height so that if Samus is crouched the transition is not triggered, but when she stands the transition is triggered. See below, the Botwoon Hallway clip, for an example.
For downward transitions, this is extremely problematic. Note X-Ray may only be used when Samus' vertical speed is 0 and she is in a standing, walking, or crouched pose.
- In sand (like the bottom of Aqueduct), this can be done RTA. See G-Mode#Crossing Sandy Rooms for an example using G-mode.
- In other cases, it is theoretically possible. This is done in the latest 100% TAS, using G-mode to enter Maridia from the top.
There are three main uses of R-mode in speedrun categories, all of which are only used in the less standard 14% categories.
R-mode clip to Botwoon
This requires using a Yard to R-mode through the upward transition in Aqueduct, collecting enough health drops to put Energy in Reserves, and then using a Mochtroid to trigger Reserves. Then this requires a very low health Botwoon (since Reserves were just automatically triggered).
Since Botwoon Hallway does not have infinitely spawning enemies, this method requires a Crystal Flash (in which one could Crystal Flash clip instead), or having more Reserve Tanks than Energy Tanks (technically, there are six enemies in Botwoon Hallway, so this works if one has the same number of Energy as Reserve Tanks but is not viable RTA).
This can be used in a randomizer. It is usually irrelevant, given the Reserve Tank and Energy Tank requirement. To have the most general example, here is a short video performing the clip with the least amount of items required:
Note in any speedrun application, one would have Morphing Ball. This not only makes the R-mode set-up into the hallway easier, but also makes the clip itself have a wider window: The window is 3 frames without morph, but 9 frames with morph. (TODO: Get a clip of the speedrun version.)
R-mode CF Suit
An R-mode forced stand can interrupt a Crystal Flash, which will give a flash suit. This is documented on the Yellow Suit Glitch page.
For the most part, this is a (possibly much easier) alternative to an Elevator CF Suit. There are some situations where an elevator may not be accessible. For example, an R-mode CF Suit can be used to eliminate the need for L+R wall jumping in 14% xChargeless, by generating a flash suit in Below Botwoon Energy Tank (and then converting it to a blue suit with a Crystal Spark):
There are some problems: in order to generate an R-mode CF Suit, the Crystal Flash must be interrupted after the Reserves have been partially filled. Therefore, this requires enough time for Energy to be put in Reserves, and then requires damage to be taken very quickly so that Reserves automatically trigger.
Therefore, most generation spots have a requirement on Energy Tanks. In particular, they will only work if you do not have too many Energy Tanks. For example, the above set-up in Below Botwoon Energy Tank requires having zero Energy Tanks.
This can be done with a maximum of 10 power bombs. This makes it possible to complete a 14% category that collects (Charge, X-Ray, Power Bomb) as the unique items. This has yet to have a known, recorded, RTA completion. Here is an example of generating a suit with a maximum of 10 power bombs:
R-mode Blue Suit
An R-mode forced stand can interrupt a shinespark, which will give a blue suit. This is documented on the Blue Suit Glitch page
This is simply an alternative method for blue suit generation in any speed running category. For example, 14% xSpeed should generate a blue suit and then G-mode to enter Maridia, so that a shinespark can be used to get to the top of Mt. Everest. This blue suit could be generated via X-mode (in fact, this can be done in Hellway, right next to where one would G-mode to enter Maridia). Thus, an R-mode blue suit is simply a potentially easier alternative.
A good place to practice R-mode blue suit generation is in Big Pink:
R-mode has many other uses, that are not relevant in any speed running category.
R-mode clips, like the example in Botwoon Hallway above, can be done in many other locations. None of these turn out to be helpful.
For example, it is possible to R-mode into the top left of Golden Torizo's Room, collect the Supers, use GT to put health in Reserves, and then use heat damage to R-mode clip back to the top left door (which does not lock). This allows collecting GT Supers in an NBMB run (if one has Space Jump, so the OoB version).
Clipping an Enemy Into a Wall
By using an R-mode forced stand and Ice, it is possible to freeze an enemy deep into a wall. With an appropriate pixel position, this allows clipping a pixel into a wall and then X-Ray Climb from strange locations.
For example, this can be done to X-Ray climb up the middle of Green Pirates Shaft:
R-mode Mother Brain
It is enough to make fewer tanks required without Varia Suit. Any combination of 4+1, 3+2, or 2+3 Energy+Reserve Tanks works. Note this requires Crystal Flashing, since Mother Brain's Room must be entered with R-mode (which will have too low of health to survive). Here is an example of the 2+3 fight, which seemingly shouldn't work since Samus has only 299+299=598 Energy:
This potentially has a use in low% RBO, or other low% categories that for some reason do not collect Varia Suit. For RBO, this would require cutting a Tank to get down from 6 total to 5. It would also require using an xChargeless base, since both X-Ray and a Crystal Flash are required.
Light Pillar Mother Brain
A strange use of R-mode, which had other uses but most of these have since had other methods found, is Light Pillar. In order to activate Light Pillar, when in R-mode hold X-Ray, deselect it (while still holding dash), and then release dash for one or two frames and re-grab dash. If successful, a weird pillar of light will form around Samus.
Light Pillar allows surviving Mother Brain's Rainbow Beam with no Energy Tanks. Thus, 0+3 Energy+Reserve Tanks works (with Varia Suit). In principle, without Varia Suit 1+5 tanks would work. Note, like with R-mode Mother Brain, this requires Crystal Flashing.
Here is an example of the 0+3 fight:
After a Crystal Flash is performed in R-mode, the power bomb location can still deal damage to an enemy. Ridley can take damage from power bombs.
Therefore, it is possible to R-mode into Ridley's Room, perform a Crystal Flash, and then repeatedly maneuver Ridley into the spot the Crystal Flash was performed. This will deal 200 damage to Ridley every single time. Thus, one can slowly chip away at Ridley's health.
This allows killing Ridley with just Crystal Flash ammo, which would normally not be enough damage.
This is not useful in any category basically because power bombs do not damage Mother Brain.
Here is a proof of concept, that at least damages Ridley a couple of times:
Also, the G-mode Ridley method will work as it is really an R-mode effect (although heat will damage Samus in R-mode); both methods may not be done simultaneously.