Below is a copypasta of my post on SDA. The mentions of real-time stuff probably don't apply, but the addresses and behaviors can probably help to some extent.
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I did some digging to come up with exactly what seeds Phantoon's actions and the various probabilities that come out of it. There are some very math-y sidenotes I have about the RNG that's used in this game (a specialized class of LCG), but the important thing to know is that it alternates odd/even, and that it has a complete cycle at each bit threshold leading up to 2^16. Another thing to note is that the RNG can be advanced multiple times per frame, so 1 frame != 1 RNG call.
So Phantoon. His first round activity is seeded separately from the second round and beyond. His pattern is determined a couple frames before he starts to move. The first thing to note is that his direction (left and down vs right and up) is seeded from the game's always-running RNG (7E05E5). If the number is even (LSB = 0) then he goes down and left. If odd, he goes up and right. Simple as that. The duration before he opens his eye, however, is seeded from a frame counter at 7E05B6. This first round has 4 possibilities, but 2 of them result in the longest pattern of 4 rotations (720 frames). The other possibilities are split between the medium (360 frames or 2 rotations) and best (60 frames) pattern. The pattern changes every 2 frames. Since it works off of a frame counter, each possibility is equally likely. The countdown timer for his eye to open is stored in 7E0FE8 (2 bytes) as soon as it is determined. The movement direction is stored in 7E0FEC as simply 1 or 0. Suffice to say, his direction does not matter at all for a real run since he'll open his eye at the same time regardless of direction, although some positions may be easier to hit than others.
For second round and beyond, his entire pattern becomes seeded by the game's RNG. There are instead 8 possibilities for these rounds, with 3 possibilities resulting in the worst pattern, 3 resulting in the medium pattern, and 2 causing the best. The actual numbers and outcomes are described below. This means that it is slightly more lenient than the first round, but getting the best pattern is still only 25%. Again, because of the properties of the game's RNG, each possibility is equally likely.
7E0FEC: Initial Direction
1: Towards
0: away
7E0FE8: counter until eye opens.
Round 1
Loads from 7E05B6, lsr, ands with 0x3
0: 4 loops, 02D0, 720
1: 0 loops, 003C, 60
2: 2 loops, 0168, 360
3: 4 loops, 02D0, 720
Rounds 2+
Pulls from RNG instead, does and with 0x7
0: 4 loops, 02D0, 720
1: 0 loops, 003C, 60
2: 2 loops, 0168, 360
3: 4 loops, 02D0, 720
4: 2 loops, 0168, 360
5: 0 loops, 003C, 60
6: 2 loops, 0168, 360
7: 4 loops, 02D0, 720
In any case, it seems highly unlikely to find a way to manipulate Phantoon in real time, and the odds are stacked against the runner. Getting perfect luck is no better than 1/16, and getting even one perfect pattern will only happen once in every 4 runs or so. There may also be a phase I'm missing yet (RNG between the rounds?) so this may not even be a complete view of the chances. In any case, good luck guys. I plan to look at Draygon in a little bit, although I don't imagine that will be as complex.
