Midlight's Deep is a ten-floor dungeon. As they said back in Warjilis, it's pitch-black in there. And even if you kill all the monsters on a level, you don't proceed to the next -- you have to find the exit on an unmarked panel somewhere on the level you're exploring.
Encounters are either super-crowded, with ten or more creatures staring you down, or are against small groups of units that have ten or twenty experience levels on you. Honestly, the ones where you're crowded are usually harder.
So why bother? Midlight's Deep has the best treasure in the game, if you know how to find it. Like many optional maps, Midlight's Deep has hidden items -- much like the volcano where we found the Materia Blade did. If you step on a tile that has an item, you're hit with a trap unless you have the Chemist's "Treasure Hunter" move ability set. (That's right, kids, no Teleporting here if you want the treasures.)
If you have Treasure Hunter set, you have Bravery% chance of getting a Phoenix Down. If you don't get a Phoenix Down, you get a treasure you probably can't find anywhere else!
I didn't screencap it, but for this dungeon, R2 is an Orator with Mettle as his secondary skill. He can Intimidate his own Bravery down to get the good treasures, then Shout it back up so he doesn't suffer permanent Bravery loss.
The stated goal for each level is "Defeat all enemies!", but it's also "Find the hidden exit before you do that!"
Assa lotta goblins.
Sometimes monsters will obligingly point out where the traps/treasures are for you. (If by random happenstance an enemy unit has Treasure Hunter set as their Move ability, they will totally swipe the item out from under you.)
She's a cursed dragonkin with ice breath. He's a three-headed flying monstrosity who spits lightning. They fight goblins!
Intimidate down...
First treasure. The Blaze Gun is like the Glacier Gun I have equipped, only it shoots Fire/Fira/Firaga spells instead. Since half the monsters in the game are weak against ice, there's not much reason to use the Blaze Gun.
Since your army is too dumb to bring a torch with them into the most dangerous unlit hole this side of your mom, spirit crystals can provide some much-needed illumination.
There are five panels that might hold the exit to the next level. It helps to know which ones they are, so you can beeline for them with, say, a flying monster.
After several crystals, it gets decently lit in here.
Not that it matters, since right after that crystal dropped, the last goblin's Doom counter ran out and he slumped lifeless to the floor. One level down, nine to go.