Holy crap, the second floor of dungeon 3 is MURDERING this game for me. Almost every single encounter starts as an enemy advantage, and at least one of my party is dead by the time I get to move, and even then my speed/hit rate has been nuked to hell so even more people are dead by the time I get to move.
Part of it is because I'm starting again from a week or two break, but god damn. It doesn't even feel challenging at this point, just a straight up battle with RNG.
Edit: Does Yukari ever learn mediarama? Media isn't cutting it anymore.
Edit 2: after dying for the 4th or so time, I charge in to the Velvet Room for fusions only to be greeted by my SECOND Marie poem of the day. It's like they want me to break my DS.
You've entered the first major difficulty spike, so you'll have to do some restructuring if you want to keep going. First things first; do you have the enemy advantage cancel navigator ability? It's called Snake Glare, and it's absolutely critical that you have this, as it cancels enemy advantages maybe 80% of the time. You can gain access to this skill by fusing Nozuchi, a level 20~ Persona. Now, the interesting thing about Snake Glare is that it will activate on
either navigator. What you want to do is give that skill to your field Navigator of choice, ergo freeing up your battle navigator to use whatever they want.
Next order of business; your team lineup. If most of the members of your team are slow, then it might be best to restructure your team. The general rule of thumb is that at least
2 of your members need nearly always outspace enemies at the start of the turn. Good characters that can do this are Yosuke, Naoto, P3MC, etc... pretty much anyone with a high agility stat. The big thing about dungeon 3 is debuffs. Enemies in that dungeon love to spam them. Masukunda, Corrosion skills... you'll need to take precaution against them. A good way of dealing with debuffs is by using P4MC's Dekunda skill. Barring that, constantly buying purifying water is your second best bet for dealing with debuffs.
Yukari gains Mediarama in the late 30s, I believe, but you won't need to rely on her if you play your cards right. Once you reach the 3rd floor, you'll be granted the ability to gain skillcards from Personas. Kikuri-hime is a lvl 37 Persona that grants Mediarama. Getting Mediarama onto a fast healer will be essential towards preventing you from getting wiped.
What's your current team line-up? Are you exclusively using one set of characters or rotating?