Alternate title: The painful events that unfold when you make one mistake and have bad luck.
When I first try this mode I was confused as to why there were 7 waves when I only fought 4 bosses, turns out, between each boss there is a set up wave that you can use to prepare for the next one, something that I really appreciate.
Armored Oak
The strats with this guy are the same as the normal variant, inflict tired so it misses more constantly and poison him. Having bomb resistance will help you endure the most dangerous of its attacks.
You will then fight one Diamond bit. I suggest to syphon it as soon as possible so you can set up without problems, the reason for this is that it can destroy itself and end the wave without you being prepared, and in this game if the enemies die to passive damage (such as poison), counter attacks or by their own hand, you will not get a turn and instead the next wave of enemies will take priority and attack you, which in all honestly is a mechanic that I dislike a lot.
Diamond Golem
The prefarable element to use against it is water, so in addition of hitting him with this kind of attacks you should also try to curse it in order to lower its defense each turn so you can have a better time killing it, I made the mistake of switching to the water bow with Anna instead of the cursed one so that set me back quite a few turns (and ultimately made me lose control of the fight for quite a bit). Also try to spam syphon against the bits it spawn, those things can be extremely problematic if left unchecked due to the array of different status they can inflict. Lastly try to have Holy resistance as the Diamond Golem strongest attacks are of that type, and being inmune to them is always good.
After the golem you will fight a claw, again use syphon to stop it from doing its most dangerous attacks so you can freely set up.
Praetorian MKII
My goddess this fights sucks. First and foremost don't kill the claws, keep them syphoned, the reason for this is that the Praetorian can spawn them at any time and basically laugh at you (which of course happened to me in this video). The list of problems with this thing includes having high evade, having a stupid attack where it shoots a laser beam and hits two characters (and can easily kill them), inflict syphon upon your whole party, and buffing itself in almost any stat. I really struggle with this one in this attempt because of extremely bad luck with the attacks it was doing as well as the syphon on the claws. That being said, the go to strat is to use water attacks and try to have it's evade lower as much as possible.
After that horrible thing you will fight a rainbloom, which you should not syphon under any circumstance as it will destroy itself and deal a lot of damage to a character, and since it kills itself you will not get a turn first when the next wave starts.
Rainbow Rafflesia
The worst boss, absolute garbage. I seriously hate this thing for one reason only, its healing attack. Its expected for bosses in this kind of games to have some sort of recovering ability in order to add strategy to the fight as well as difficulty, but this one went overboard. The healing attack of Rainbow Rafflesia not only heals, but also increases its magic attack and defense, it cures all of the negative status and debuffs it currently has, as well as casting bless upon itself so you can't inflict status nor dispel it for NINE TURNS, and this doesn't apply only for itself, any rainbloom currently on the field will receive the aforementioned buffs. Want to know the worst though? It can use it turn after turn, if you are unlucky this thing will heal itself by an obscene amount of life and increase its attack (and of its cohorts) to high heavens to one shoot your party without any problem (which is exactly what made me to lose in one of my attempts when it nonchalantly used it for 5 turns straight). Rant aside, the strategy against it is to have a lot of crowd control attacks (of the wind element as they are all weak to it) as well as being really agressive so you have less turns to worry about dying and by extension, less chance of seeing the healing attack.
Overall I was very happy to have gotten this one so quickly (only three attempts), the latter bosses could have been a wall to overcome for more time but thankfully I was able to get it done due to developing strats with the equipment and attacks.