Re: Princess Sacrifice
I actually beat the final boss's first form (all 999 HP) by being a lvl 18 Knight (+defense class).
I used all the +Def "knight-like" items (Armor, Helmet, Leather Stockings, Silver Sword, original short-skirt from the beginning of the game). The key was extreme-spamming of the "defense" button. Whenever the final boss used lightning, it'd only do 5 dmg, and whenever the final boss did the "5x multi-strike" attack, it'd only do 1 to 2 dmg per strike. Regular strikes did between 0 and 1 dmg.
Of course, if I got impatient and aggressively attacked, the boss would basically one-hit KO me. So most of the time was spent spamming the "defend" button. The very very little damage you take is easily auto-healed off as the goddess heals you. The boss eventually starts raping you, but that only gives you the ability to cast lightning (after a few iterations anyway). It also depletes the final boss's MP pool. So just spam defend until the boss falls asleep to the rape, and smack him afterwards. (Use the 3MP spell to reliably untangle yourself from the tentacles if necessary)
If the Boss's MP is low enough that I know its safe (below 5 was my heuristic), I'd start striking him with the sword for ~3 to 5 dmg. If the boss's MP Pool is close to zero AND I have the 8 MP needed to cast lightning, I'd cast lightning for some 30 dmg. The only tricky thing was that lvl 18 Knight only has 15 MP, so I needed 3 turns: Cast Lightning, then I used the super "all heal" item, and then I cast lightning again.
Be sure to save up the "All heal" item btw, it gives you max HP, max MP, and max LUK, recovers all your clothes and removes you from any status condition. There are only so many of those in the game however, so be sure to save them.
The rest of the damage was from the goddess auto-attacking. Just sitting around defending is enough, because the Goddess is going to heal you and auto-attack the boss for some damage. Goddess also has a few spells that will deal 20+ dmg to the boss in one hit (even when the boss has +defense spell up)
Managed to kill the final boss with 999 HP, all it does is make the boss angry and auto-kills you. But at that point, the "2nd fight" has the boss at only 50 HP, and it was pretty easy to just cast lightning twice without dying at that point. (both strikes did 30 DMG).
Knight didn't seem like that good of a class for most of the game. Most of the damage was from the goddess assisting you, but I know this strategy is basically foolproof. It just takes a long time. But nonetheless, if you want the Below-40 ending, you're gonna have to do this. (You need 60 Holy to transform into "uber mode").
I have yet to beat the "final final" boss of the Below-40 ending however. I'm planning on just going through the "New Game+", level up a bit more and then maybe attempt the Below-40 ending after a 2nd iteration.
for the equipment, i'm using only equipment that doesn't decrease my stat
Note: the point of the "sex items" is to increase your MP outside of battle. If you click on Feena's breast or Crotch while vibrator is equipped, she gets +1 MP about half the time. If you aren't the prostitute class, you should be able to get +4 MP before casting the 3MP status-heal spell, which resets the sex-meter. So some classes can manage to "break even" and recover MP through the vibrator or dildo.