First of all, what’s a „turn“? Whenever it’s a character’s turn, no matter if friend or foe, and no matter what the character is doing (attack or wait or whatever), the turn count goes up by 1. So I guess it’s impossible to clear the cyclone chamber within 10 or 12 turns. You must clear the elemental chambers within 140 turns.
Some stages have a very low turn max for S rank, so don’t underestimate that criterion. In the following battles, if you want to get all chest and dig items, I recommend you to kill fast and don’t waste any time: Middleport Secret Room, El-Eal 1st battle, Merseto, Caleron 2nd battle, Haruna and Graska Palace.
I made a test just to confirm the stage rank formula. I used Obel Ruins level 1. My characters were Lv27, the enemies Lv28 or 29, I forgot. These are the requirements to get S rank there:
Turn count: 50 -> Be fast! I think there’s no way to get chest and dig items plus S rank. Attempt S rank either by ignoring those items or when you already got the items from that configuration earlier.
Total damage: 100 -> This means damage taken/suffered! There is no total damage dealt criterion! You may not suffer more than 100 damage. Healing and switching won’t help afaik. As you can see, the your levels (and the enemies’ levels) the harder to achieve S rank, unless you have plenty of awesome equipment.
Damage average: 70 -> This means damage dealt! And it’s the average of all actions that (can) deal damage. Putting negative terrain under a foe doesn’t count, it’s just a byproduct. If the enemy evades, it counts as an attack that dealt 0 damage. As you can see, waiting is better than dealing too few damage because waiting doesn’t count and thus doesn’t lower the average.
Positive terrain: 15 -> It says you must end a turn on positive terrain, so I don’t know if it helps to put positive terrain on your allies. This may be easy to achieve, but in levels like this one where turn count is low, it can be difficult to reach the positive terrain number while meeting the requirements for the other criteria at the same time.
Total experience -> 500 per enemy, so it depends on number of foes. I don’t know how reinforcements are handled, they probably count as well, but only if they appear. The safest way to get S rank is to use characters with lower levels by 1 or 2, but not lower than 3. If the enemies are between Lv24 and Lv26, then use Lv23 characters, and so on.
Results of 1st try (I only used 4 characters, 1 on owl)
Turns: 66 = B
Total damage: 0 = S
Damage average: 1028 = S (far more than required, good job Lazlo)
Positive terrain: 17 = S
Total experience (15 foes, I need 7500): 6200 = A
-> formula: (30+0+0+0+10)/5=8 -> stage rank A
That was bad luck, because if I had needed 1 turn less, I had got rank A in turn count, then the formula would have been (10+0+0+0+10)/5=4 -> S rank
Results of 2nd try (this time 8 characters to get the positive terrain count faster, 1 on owl)
Turns: 32 -> S
Total damage: 0 = S
Damage average: 642 = S (still far more than required)
Positive terrain: 15 = S
Total experience (12 foes, I need 6000): 8834 = S
-> formula: (0+0+0+0+0)/5=8 -> stage rank S of course. Notice that you can get A rank in 2 criteria and still get stage rank S, but if you get B rank in just 1 criterion, you can’t get stage rank S anymore.
Turn count: Generally easy to get S rank. If you try to get S rank as well as chest and dig items, then it can be difficult in some stages. But in most stages it’s still easy.
Total damage: That depends primarily on your strategy, and secondarily on defense stats. This is arguably the easiest to fulfill.
Damage average: Difficult in early game where you must rely on extra damage from coop-attacks. From mid-game onwards where you have plenty of ways to increase damage, it’s a piece of cake.
Positive terrain: Only if turn count is low, this might be a problem. It will probably happen more often that you finish a stage too quick.
Experience: As long as you don’t overlevel your characters, it’s easy. Take extra care for Kyril (required in every story battle) and Lazlo (makes difficult stages like Graska Palace easier to get S rank).
One more thing…
You can experience by either dealing/healing damage, or by everything else except waiting. In the former, the amount of experience gained depends on the level difference between character and target. If the level is equal or of the character has a higher level, you will get almost nothing. Killing an enemy gives extra Exp.
In the latter, it depends on the stage level, some virtual level, somehow linked to the average of the enemies’ levels on the one hand, but fixed on the other hand (doesn’t change if you kill all high level enemies or so). For example: if your enemies are Lv30, then the stage level is about Lv30, let’s say it is. A Lv30 character gets 15 Exp, a Lv29 character gets 110 Exp, a Lv28 character gets 155 Exp, a Lv27 character gets 190 Exp, and so on. There’s no way to get extra Exp, that’s why it’s harder to level a support character than a fighter.
"Within the four seas, all men are brothers" Shuihu Zhuan