Twinrova is the final boss of the spirit temple, and immediately follows the Nabooru iron knuckle mini boss fight. The arena consists of 5 tall square platforms, a large one in the middle, and four smaller ones, each a jump’s distance away from one of the middle platform’s sides. The walls at the corners of the middle platform are climbable, and hookshottable, so usually players will begin the room by hooking up to the top of the wall. The fight begins when Link enters a small zone in the center of the middle platform.

The fight takes place in two phases. For a video representation of most of this information, check out this video: Twinrova Tutorial - Beating the RNG
The boss consists of two witches that fly around the arena shooting a beam of fire or ice which you must reflect off your mirror shield to hit the opposite witch. In order to reflect the beam, you must crouch behind your shield while Link is facing within 45 degrees of the witch who is shooting it. Tilting your shield’s aim to the sides to catch the beam is not possible; all that matters for the initial catch is where Link is facing.
Where each witch flies and when they shoot has random components, but these decisions are telegraphed enough that the player can adapt in real time to most situations. Here is a description of each witch’s behavior (they both behave identically):
Here are some strategies to help mitigate the random nature of the battle:
Once four hits have been dealt in total across both witches, and there is a moment where both witches are flying idly, phase 2 will begin. That wording is important because it means that the end of the phase can be delayed if both witches are not idle. If you deal the 4th hit to witch A, she will take some time to shake off the hit before becoming idle again. If witch B decides to try to shoot at you before then, the end of the phase will be delayed until the shot is done and, again, both witches are idle at the same time. If you notice one of these “fifth shots” about to occur, shoot your hookshot at the offending witch to spin her around and cancel the shot. Assuming the other one doesn’t take that momentary opportunity to also begin shooting at you, the phase will end.
In this phase, the witches merge into one and begin flying exclusively between the outer four platforms, shooting a magic attack of either fire or ice from each position. Your goal is to absorb three in a row of the same element in your shield, after which a burst of energy will be released from the shield which will stun the boss if aimed properly. She has 24 health, and will take damage from melee weapons only while stunned from the beam.
Here are some strategies and information for this phase: -Before ever dealing damage to her, she will always shoot the same element three times in a row. Usually it only takes one cycle of damage to kill her, so a speedrunner shouldn’t ever experience the random shots which come after dealing damage unless they’ve made a mistake.
After shooting a beam, twinrova will take some time to select and then fly towards the next platform to shoot another. If you stand far enough away for the beam to take a while to reach you, you can shoot your hookshot toward her right after she releases the beam and before it reaches you. This causes her to spin and then select a new platform a couple of seconds sooner than she otherwise would have. Standing very far away has no downside, so being safer is better here. Again be careful to not press shield one frame after releasing the hookshot.
Standing very nearby to one of the side platforms (within 300 units) that twinrova is not currently occupying will give you a 1 in 9 chance for her to reselect the same platform she is already on. This cuts out travel time between beams and leads to what we call a phase 2 double. You should always try for this by being near the edge of the center platform during the first beam of the phase. However note that it causes twinrova to rise a bit higher than normal, so your muscle memory for where to release the energy beam from your shield might be off after doing this. Going for a triple is not advisable due to how high she rises being really awkward to deal with. Not to mention it would mean you are by definition really far from her when absorbing the third beam, and you want to be very close to her instead.
When releasing the energy back at her, you can do so while standing on the corner of the same side platform that she is on, and aiming your shield straight up from a crouch. If you don’t have the time to get there, you can do it from the center platform, and then hookshot her body to get over there to deal sword damage more quickly than jumping over.
Although arrows, bombs, and bombchus can deal damage, you will primarily be using a sword item as other items cannot deal the finishing blow. When dealing sword damage during the stun, you probably want jumpslash damage stored to your crouch stab. Using master sword/deku stick/megaton hammer, each stab will deal 4 damage. Since she has 24 health it will take 6 stabs to kill her. Luckily, 6 stabs is exactly what you have time for before she gets up for another round. Don’t mash the stabs though, because hitting her body with the sword during her temporary invulnerability between hits causes hit lag. Learn the rhythm and just time your stabs.
Link will always appear in the exact same position with exactly the same camera when the fight is over. This is good for initial-position setups for the blue warp cutscene skip in runs which allow it.
Some examples are shown below.
If you deal the final hit melee on twinrova while your shield is still hitting her with the magic beam, you can wait around in the arena for a while for “ghost twinrova” to appear. This is an invisible twinrova who will begin battling you again without warning. Defeating her will spawn another heart container, and this can be chained indefinitely, though it is very slow due to the long wait. Since the mirror shield doesn’t emit the beam for very long, you can’t do this with a one-cycle strategy. Rather, you’d need to do most of the damage in one cycle, and then just do a final hit quickly after stunning her in a subsequent cycle. Shown here :
further documentation on this topic can be found by mzxrules here: https://pastebin.com/beph6uSC