I'm pretty sure this is consistent, I practiced it over and over by just restarting the checkpoint for the boss fight before the end credits sequence begins and can get it easily 9.999/10 times.
https://streamable.com/jtzlr Ignore the audio, I was listening to a friend's stream while practicing
After the predalien takes enough damage, he'll have a little over half health, he will run away and jump up to start the next cycle after romping around a bit. I've seen that two charged plasma caster shots and three light attacks push him over the edge and make him run. Also, if he knocks you down and does a grab attack he seems to just run afterwards. Also also, dipping him into the lava causes him to immediately run when he jumps out. You both always start in the same position and from what I can tell he seems to randomly choose a direction to get to you, on your left on your right or straight towards you. If he goes to either side it's safer to wait until after he jumps again because he lands on breakable flooring. If he jumps straight towards you he lands on an invincible platform so you can immediately start firing. Hit him with two charged plasma caster shots and two light attacks. If you do fewer he's less likely to start a charge attack, after which he'll always roar which will waste a bit of time, but you'll have to get more damage in later to make up for it. I like to go for one now because I feel it helps just enough to make for an easier kill later and is often fast enough to not allow him to charge attack you. Jump onto the nearby breakable section of the platform just to the right of the screen when you spawn in and he'll follow. When you land immediately turn and charge a plasma caster show aiming at the floor where he'll land. If you jump too far forwards he may jump so far onto the platform that he'll be on the invincible flooring and you'll probably need to jump back and forth to reset his position. Shoot at his feet once he lands to hit him with the splash and dip him in the lava for a lot of damage. Where and when he jumps back out feels totally random but he always seems to try to jump up to the ledge right above where you spawn so just go back there and wait. When he comes out burst him down with plasma caster shots, melee, and spears until he dies. You ought to be able to guess good enough where he's going to jump out of the lava at by his screeching audio cues. If you miss his feet with the plasma caster shot when dunking him in the lava it's still doable if you REALLY wail on him after he gets out but it's a lot tighter, maybe not doable if he gets out too close to the starting ledge. I've tried using mines at the base of that ledge to get more damage on him but he doesn't always jump up to the ledge from the same place and is so fast he can usually just run and jump past them without taking damage. I also haven't compared the time of this to the normal two cycle method so I'm not sure what kind of time save potential this has, though it's probably not very much.
Have you tried that out restarting the level? It's possible that starting from the checkpoint there is giving you a fixed RNG that'll let you consistently do that
Did a bit more testing, like 3 or 4 playthroughs of the last level and he seemed to always try jumping up the same ledge by I spawn right below to start the second phase. His pathing following you seems pretty consistent other than at the very beginning so baiting him onto the breakable platform is consistent. His spawn point when he jumps out of the lava still feels totally random though so you'll have anywhere from plenty of time to barely any to get in all the extra damage you need.
In this he went right instead of straight so I had to wait to use the plasma caster and I stuck around too long and he charged a hard attack. It looks like even when he misses you with that he stops and screams for a bit so I'm considering just not punching early on if he doesn't come straight at me. Even if you get hit by the charge attack though if you're in a shift jump then you won't get knocked back and there is no way he'll ever do enough damage to kill you. I've also seen if you can hit him as part of him is exposed in the lava you can get a little extra damage in, but it's pretty inconsistent and hard to do. I missed it here, but since you're not doing anything else I figure it's probably worth at least trying.
I've gotten it to work a majority of the time, unless the predalien is close to the right side edge of the platform you spawn on. If that happens, he'll land behind you after you jump to the platform and mess up the setup. To get around that, I usually lure him further back on the platform and shoot him before jumping over.
