Episode 5, Stage 3
This is the First Great Levelling Map in the game. I personally recommend
avoiding serious levelling (beyond what's necessary to get you through the
plot alive) before reaching this point, because the rate at which you
gain levels will make any power levelling before this point feel like a
waste of time.
Once you reach this stage, it's difficult to miss its potential for
experience-filled goodness assuming you make two observations:
(1) Everything except for a character or enemy located in one specific panel
is invincible.
(2) Throwing one enemy into another produces a new enemy whose level is the
sum of the previous two enemies.
The method for power levelling here should be immediately obvious. Throw
enemies together until you've obtained one of the desired level, then throw
this enemy into the one non-invincible panel. Smash it. Repeat as desired.
The only thing to watch out for is that an enemy may become impossible for
your characters to damage if made too powerful--if this happens, you get to
reset/give up. Also, if you get to the point where combining all the enemies
produces something too weak for your needs, you can remedy the situation by
raising enemy levels through the Congress.
An additional tip here--there tends to be a single enemy on this stage which
has particularly low defense compared to the others. Using this one as the
high-level target will make it easier to damage and thus speed up the
process.
If you have any trouble progressing through the plot before Episode 10, this
is the map to fall back to and build yourself up.
Mix that with unlimited movement/action and you've got levels 4 daiz.