...has a boss that has 18662 Turn Recovery. That is a ridiculous amount.

I think the game assumes you already have some Mirage Lances around, but even then, it looks like that may not be enough.

For reference, a Dragonewt Fighter should be able to deal, with a Mirage Lance:
(70 + 5) = 75 damage per hit
75 * 20 = 1500 per attack (not counting mastery skills)
75 * 25 = 1875 if we take into account 5 casts of Orath
1875 * 1.5 = 2812.5 for a level 425 Fighter.

That is not enough for a party of 6 level 425 Dragonewt Fighters to outdamage the boss's health regen. (Getting an Innocent Fighter that can cast Orath requires using the Mirage Shield to randomly change class.)

So, how are you supposed to defeat such a beast?
(Does the 3DS version let you alchemize the Mirage Lance? Double damage against Gods might help here.)

You forgot about spells and spell mastery, 3 Mages with max Spell Mastery (does it require around lv.2000?) without trinkets should be able to burn through this amount of recovery.

Fighter also should be able to do over 7k damage at such setup with max mastery (324.3%, at what level does he get it?)

Tackle should also give chance to halt boss' regen at 30% per char (88% chance if all chars have that skill)?

What is that 3DS boss in question?

The 3DS boss in question is the one at the end of this video:
https://www.youtube.com/watch?v=do0SKqqdZ-0

The 324.3% bonus requires is at the level cap of 16,849. At level 425, the bonus is only 50%. (There is a formula for mastery bonuses: bonus = base * sqrt(level - 25). Base is 2.5% for the Fighter's Physical Attack Power +1.) (Also, in the 3DS version, apparently all races level more slowly, so fighters can't surpass level 16,289.)

A max level mage gets a bonus of 6% * sqrt(15139 - 25), which is 737.6%. The maximum amount of AP possible is 142 AP (assuming a level 15,139 Alchemist), which is enough to get a Rainbow Charm to give a 484% bonus to lightning damage. With those bonuses, I think the average damage is still under 3000.

One more thing that might help: In the 3DS version, you can change your EX skill for a fee. Therefore, you could give your fighters Mark of Ruin in order to get the 50% damage boost, and maybe add War Rite to that for more damage. Then again, the tackle idea sounds good, and a priest with Immolarati could take off half the boss's HP in one round. Just make sure to have enough Miracles to supply her with MP so she can keep using it.

Also, it might be a good idea to kill the boss's helpers first. Judging from the video, one of them "only" recovers between 2k and 3k each round.

Found about this boss here. Symphorien Neff Sea with Sukia and Force in front (with their stats at very bottom of the page).

Also need to mention that a lot has been changed in 3DS version (all item stats, monster stats, etc.). Might make this boss much more approachable. According to wiki, there were so many changes, that I basically disregard 3DS version as true Elminage Gothic (just like I disregard FF XII Zodiac version as true FF XII) :)

The Youtube user posted a follow-up video in which those bosses are defeated.

https://www.youtube.com/watch?v=6njYnHU9VpY

Anyway, it appears the player did make use of Tackle.

I noticed the player mentioning having to raise enemy AC even with at least one character who was over level 400. Also, the enemy with no turn recovery could use Summon Judgement (instantly kills the party's current summon) and the one with about 2400 turn recovery had Swallow Return (hope you have Swallow Killer). The bestiary entries are shown at the end of the video.

I should point out that, on lower HP characters, my cleric can actually heal mare than this player's Hand of Kindness healing. I think I may post a detailed analysis of the Cleric class later. (I have used one continuously from the beginning of the game up through Ibag Tower 6F, the furthest I have played.)

One interesting version: one of the summons the player used actually had over 9999 HP. Is this possible for summons in the PC version? (I know regular party members can't go past 9999.)

I saw there were 2 summons in use in last fight and it was hard to see their HP in that video, but i think I saw their HP in 4 digits.

3DS version is just way too different. Some dungeon floors are totally different, a lot of enemy formations are impossible to encounter in PSP/PC version, and so on. Only thing which PC version has from 3DS is soundset (PSP soundset was easier on ears).

Caps are theoretically easy to change in CHR.csv, but I think anything that changes variable's type is no-go (so you can change max HP to 65535 but not above). 3DS added (unlocked) some new races, that might have caused unintended cap changes in csv file. And there I thought that you have already finished game at this point :)) I myself took break from Elminage because of various stuff (disassembly files of Phantasy Star II, III being one of them, so beside PS game mechanics I have actually learnt a bit of Assembler! At least I think so...), so I need to catch up with my characters a bit.

I actually have taken a break from Elminage Gothic, mainly because things are rather ridiculous. Remember my previous post about the Archer Polete enemy? (Also, I bought Ys: The Oath in Felghanna during the sale and decided to play it. Good game, but isn't even in the same genre (by my definition) as Elminage Gothic.)

As for the summons, one of them (Gaia, I believe) had over 9999 HP, but the game only displayed 9999. I know this for three reasons:
1. Strange Miasma Wave did over 5,000 damage.
2. The healing spell, which was obviously affected by Hand of Kindness, healed over 2,000 (when the regular party was healed less than 1,000).
3. Sometimes the monster would be at 9,999 after taking a hit.

The other monster summoned was, I believe, a Star Gazer, which is a palette swap of the Archer Polete, and is apparently more dangerous (as if Archer Polete weren't deadly enough in the PC version).

By the way, in Phantasy Star 3, I have beaten the final boss without spending any resources. That means no TP use and no use of consumable items. (I did use non-consumables, however). Can you do this at a reasonable level?

Maybe. Either it is video quality, my eyesight or 3DS, but for me it is hard to watch those 3DS videos, especially in Japanese -.- I even wrote down Symphorien's equipment in Katakana, but it didn't make any sense...

Also I think this new 3DS boss was needed, because true final boss (of PSP/PC version) is relatively too "weak" in revised 3DS ruleset. It depends a lot on good level ups and luck in actual fight. Currently I am doing replay of PS3 with perfect HP+TP+Damage+Defense for Mieu, Wren (and later - 3rd Gen). I have beaten PS3 last boss without using any items (but used Gires), as that's the way I play - I try to not use any items unless it is entirely unavoidable. Difference between perfect stats and worst rolls is huge for some characters.

If under non-consumable you mean ForceShield, then such challenge is possible at lv.1 (you can keep Mieu and Wren dead and amass lots of Meseta to buy best gear), just need tons of luck - boss must never use any technique and attack only your Main Hero at sustainable damage levels (Body hits for 38-47 against 308 Def, and RightHand hits for 15-18; 308 is max Def of Lv.1 Sean who has worst HP/Def as 3rd Gen Main Hero).

Actually, I think the non-3DS final boss may be the more difficult one, mainly because of all the status effects. Notice how many times the player used Miracle for healing. The new 3DS boss isn't that difficult from a survival standpoint; doing damage fast enough is the challenge. I think that boss was added to give the player a chance to make use of the Mirage Lances that can be stolen from the non-3DS true final boss. Actually, by non-consumable I am thinking of two items that are even better: the Force Vest (Rever 10) and the Royal Vest (Nasak 50, which seems to always work). I don't bother healing living characters most of the time. If somebody dies, I use the Force Vest (usable even out of battle by dead characters) until it works, and it ignores poison. If multiple characters are low on health, the Royal Vest can fix that, and then the Force Vest can be used to heal that character.

One more thing about Phantasy Star 3: Forza really should have been named Vol. Enemies killed with it do yield experience, and it doesn't work on mechs. It is an incredibly useful technique, provided your main character isn't Ayn.

Excuse my intrusion, but I just wanted to point something out. As the 3DS game is called "Elminage Gothic 3DS Remix", it would be safe to assume that much of the content of the game would be changed and/or mixed around. Your opinion on whether or not that is a good thing is still sound and justified, but I just wanted to say that the name of the game gave you fair warning. Carry on! ^_^

It is, however, interesting to see what has changed as well as what hasn't. One interesting example of something that wasn't changed is the Sacrifice skill. According to the Japanese wiki, it is still only found on one of the premade characters and (without hacking, which is harder to do on the 3DS) not possible to get on anyone else.

You don't have to run away... :)
Sacrifice skill is perhaps a left over, just like mention of day/night cycle playing any role (EX-Skill ID 127 "Sun's Blessing" mentions it, but you can't get this skill by honest play). And it looks like Elminage 3 (not sure about 2) had day/night cycle.

Elminage 1-3 had a special twist though, you had a competition party, which you could randomly encounter. This party keeps getting stronger each time you encounter it to the point of having no chance to win.

I found funny video of one boss fight in Elminage 3. Boss is passive until 2 of his helpers are dead, then he goes on rampage. That one 61k hit was something completely unusual. I think it had to do something with "Glutton for Punishment" and one of the characters having only 15 HP.

Glutton for Punishment was likely part of it, but there are also special blessings your characters can get in Elminage 1 through 3. There are 6 of them, each can only be on one character, each character can only have one, and characters resulting from marriage (and Spirit Pact?) can't have any. The blessings are as follows (this is all according to Japanese wikis):
1. More damage at low HP. 5x damage when HP is very low.
2. All healing restores full HP. Who needs a Cleric with Rafiereed when your Valkyrie can fully heal the party with just a Rafelima? (Then again, in Elminage 3 it looks like a high level Cleric may be able to heal 5 digit HP to the entire party without the blessing.)
3. Infinite consumables. Suddenly, Servant becomes one of the best classes! All the Full-Health potions that you will ever need for automatic healing.
4. Attacks ignore status resistance. That Ninja with 50% behead chance? That's now 50% behead against *anything*, superbosses included.
5. Always act first. This could actually make Cleric worth it to heal quickly (while another character gets the healing one to heal cheaply). Also works well with Absolute Defense.
6. Never lose stats at level up.

As one can see, they range from nice convenience to game-breaking. Just imaging: 95% beheading that *ignores* enemy resistances.

guy use absolute barrier, so everyone ''skip'' their turn, except his bard it would seem he has the blessing of going first... I killed that boss and he's quite nasty hehe. not the hardest in the serie though, considering there's a trick to get at max level without too much trouble.