Nagas can be a challenge if you are at a low enough level. They cast LIT2, among other things, so use ALIT. Watch out for Waters while you're at it, you can't run from them. Use Ice spells to take them out.
Here's another group you can't run from. A good plan would be to just kill off the red ones with a LIT2 spell (use the Zeus Gauntlet) while killing the wizzies with weapons.
Speaking of running, I suggest you do run from any group containing Lobsters, as they can poison you. If course if you aren't annoyed by that sort of thing, use Lit2 to thin out their ranks.
Ghosts are the big mean granddaddies of all undead creatures. They are the most powerful (attack-wise) non-boss undead, they usually come in packs of 5, and they don't have any spells to slow them down from kicking your ass! Worst of all, they are all over most of the floors here. You can't run from them, so you'll have to fight. Powerful Fire and Harm spells can kill them quickly, but if you're not careful they can kill you just as fast.
Here is what my party looked like after the battle that picture was taken from.
This floor is full of good treasures, but it's also full of ghosts, so watch out.
This is the second best armor in the game. Watch out, there're Sea Snakes to the left of it.
Yuck, don't bother with this one.
This handy device will cast HRM2 when used as an item. I like to give them to non-magic-using classes.
This is one of the best weapons in the game, because it casts FIR2 when used as an item. I usually give it to a Black Wizard, but you could also give it to a non magic-user.
'At's a spicy meat'a ball.
Here's the staircase to the fifth floor.
There aren't any enemies on this floor. So sit back, hang out with the fish-babes, and get all the treasure.
This is the best bracelet. Give it to your highest non-armor-wearing person.
Uh, yeah, that's exactly what we've done.
Whoa, sucks to be you.
Yeah, I'm sure she did. ...fruitcake.
That's not all I can do underwater baby.
Head up thiswise to reach the room with the Slab.
This is the best helmet in the game, for helmetting purposes anyway.
This is nice, but a ProRing is better.
Oooh, the Slab. Take it back to your good friend Dr. Unne.
Don't want much, do ya'?
Yes, we are the legendary....
Not bad at all.
Yes, I'm afraid so.
Why would you even bother putting that in a chest?
Ohhhh, I guess we should go kick his ass, right?
Don't worry baby, I'm here for you. I'll make it all better.
Good to know.
This is the second best shield.
If you have it, cast EXIT (or WARP a few times) to get out of here. Otherwise just walk out the way you came. Head out to Onrac to save and such.