A great majority of the Jalhalla fight is based around speed and efficiency. Jalhalla is composed of 15 poes, and will always reform once 5 poes have been defeated. It is possible to kill more than 5 on each cycle if you manage to kill the 5th poe and other poes for that cycle on the same frame. If you have not killed 5 poes by 15 seconds after the cycle begins Jalhalla will reform regardless of how many poes you've killed.
Although the Jalhalla battle is relatively straightforward, it does contain a number of crucial limits that must be kept in mind. Firstly, the minimum number of cycles that Jalhalla can be defeated in is three (in an RTA setting, TAS could technically get one cycle). As he is composed of 15 poes, this means that typically in each cycle you can only defeat a maximum of 5 poes before Jalhalla respawns. However there is a slight exception: you can kill 6 poes in one cycle (by killing the 5th and 6th with the same blow). But, this means in the following cycle that you will automatically be limited to killing only 4 poes. This is a relatively rare happenstance though, and most of the time even if you deliver a finishing hit to a sixth poe it simply will not die and Jalhalla will respawn.
During the first phase, you are intended to quickly reach a beam of light and use it to solidify Jalhalla. If you are not fast enough, two of the beams will randomly fade away. Once you have made him solid (the second phase), you must toss Jalhalla into one of the spiked pillars to split him into 15 poes. The power bracelets are needed to be able to lift Jalhalla, and so the power bracelets can not be skipped in an All Dungeons run.
However, if you got the Light Arrows early, then you can instead simply shoot Jalhalla with a light arrow, which will instantly solidify him. This is much faster than using the mirror shield to reflect the lights.
The best and quickest way to dispatch of them is by throwing 3 bombs in different directions during Jalhalla's "explosion" into multiple poes. While you go around killing poes the bombs will hopefully kill some for you.
With a good aim, arrows can also be used to kill the poes in the second phase. This doesn't necessary save time though, unless you are very quick at aiming — as it takes two arrows to kill one poe. But due to the mechanics of how arrows continue moving and having the potential to deal damage until they hit a solid surface (like a wall), you can hit poes in one shot if they are lined up with each other. A fire arrow does however defeat a poe in a single hit, but it uses magic.
Curiously, if you defeat a poe with a light arrow, then the poe isn't considered defeated, and the cutscene of Jalhalla's reformation becomes much longer than usual, and so is a waste of time.