10~12F puzzle... I've gotten to the relay point on 12F. The new battle music for this part is totally awesome, and its perfectly placed too; DAMN these random battles just got a lot harder. High-HP stuff, and physical attackers that move before everyone other then Chen, STOP KILLING MY SQUISHY PEOPLE IN THE BACK RAAAGE
Okay, this is testing my patience on exploring every nook and cranny. But I will survive~...! 
Yeah, I think everyone gets sick of those 3 floors long before they are done with them. You should try and get every last bit of the map though, there are 2 event chains starting on those floors that result in optional boss/characters that join later on. In addition a chain that starts and ends on the 10th floor (which is accessable by the relay point mentioned, backtrack and go right from the bottom of the map where there are 3 opposite-polarity blue orb door thingies, bear in mind though, that you need to have all 3 colors turned off to make the trip worthwhile, the "all switches on" doesn't turn them off if you use it twice, you have to manually turn them all off the slow way from the ordinary start of the dungeon, then teleport up to the relay point. It's a pain in the ass, but the character you get is useful IMO.
If it wasn't for the music change and the enemy change midway thru, those 3 floors would be intolerable imo >=P.
Phew, beat the 12F triple boss finally.
All it took was gaining a few levels and about 83k-ish skill points to spend on boosting a few key characters' MND stats.
Took out the rightmost boss first. Things are only going to be harder on myself the longer that boss stays alive. Buffing defenses is critical too. Good thing with enough defense buffs my 10F girl gets damaged by very very few attacks, if any, and Meiling can basically cancel out any damage to herself with her self heal.
I had about 3-4 attackers for the fight, but only two were really attacking almost all the time. The others I brought in when had to swap out one of those two to let their SPs recharge.
Everyone else? Either buffing or being switched in to let others regen up.
Once the rightmost girl kicks it, I break out the ol' caluculator and keep track of leftmost boss's HP. After knocking off close to 200k, focus put on middle boss.
Once I have Marisa and Patchy 100% buffed on MAG and at least one other person at high buffed ATK/MAG, I swap them all in after both bosses have recently taken an action, have Patchy fire off Royal Flare, Marisa Master Sparks middle boss, and whatever else I can fit in before a super attack comes from a solo boss and wipes me.
Of course, I never got to use Marisa's Master Spark because Royal Flare wiped them both out at once.
Saved afterwards, went to 13F...oh god this looks promising. Enemies are promising too. Oh god Swordfish that can knock off half my 10F girl's HP with their WEAKEST attack and are god awfully fast.
I'll start braving it tomorrow.
Did you get the 8th floor optional character yet? It should be doable now if you haven't done so yet. Also, make a habit of spending some points in MND, it's a much more useful stat than mag or attack imo for tough bosses (though not as much for trash).
Floor 14 swordfish are BS >=P. Once you get high enough a level (assuming you aren't already) that they can't 1shot your squishies, or 2shot your tanks, it's not so bad, but until then. siighhh. The knights on that floor also have a chance of dropping a blue saber (name is slightly diff if you have the older translation patch still), which is basically a cuisenart blade on steroids, very nice for its time.
Speaking of which, does anybody know what solar demon kings drop? I'm getting oodles of drops from floor 19, lots of +40% attack items (I forget the name), glaives of pain, etc. Useless crap, but I never got a drop from a solar demon king, it has to be good since those baddies are basically random minibosses.
