I know this game is a few years old, but I just got ahold of it again a week ago and finished it. I enjoyed it a lot and I thought it would be nice to share some information and tips about what I've encountered.
First of all, it took me 55 hours in-game time. I think about 35-40h for the story, and 15-20 for the chests/mirages/board mastering/miniventures/murkrifts/hidden areas cleanup.
Here's the link for the checklists https://mega.nz/#F!3I8iyYhA!B_aDNRPILrMhtY9w4w-Esg
There's one for chests, mirages, miniventures, hidden areas and murkrifts. For the mirage boards, I just added a // MASTERED myself at the end, I suggest doing something similar. For miniventures/mirages I recommend double-checking in the in-game adventure log and mirage's encyclopedia in the Twin's Room.
I recommend using some text editor like Notepad++ for the checklists instead of Windows Notepad due to being able to have multiple files open on the same instance of the app (otherwise you will have 5 different Windows Notepads open).
And here are my tips:
Mantain a checklist of your progress - specially chests. You will avoid unecessarily re-checking all towns, regions and dungeons for these few missed chests (there's no in-game counter or anything) and other collectibles.
Try to do as many miniventures as you can along the way, in the end-game some will be tedious because spawns are rare. For the Mirage Hunter one (12 quests total), just wait until you have all the mirages and do them all at once with the help of Seraphones.
Capture mirages as you go, but don't overdo it. One mirage for each family is enough - for example a Minichocobo will be able to be transformed into a Chocobo, Dark Chocobo, Hyperion and Mecha Chocobo. Once you progress through the mirage board, you will be able to transfigurate it to the other families and it will be easier to see in your collection which families are you missing to master the boards in the end-game.
You can try murkrifts as you go if you have enough level, but otherwise just leave them for the end when you re-trace missing miscellaneous trophies. You will have to re-visit some dungeons even if you keep track of the chests due to some hidden areas being unlocked later on.
The first "ending" is doable at around level 50 of your party. The "true ending" is doable around 60-65 and for the XG boss in the EX Dungeon Z I would go past level 80-85. It's doable earlier, but it'll take too much time compared to grinding for an extra hour or two, which you will need to do anyways.
When you are capturing the "seven of the Pleiad" for the true ending it's possible that in the coliseum you kill Ramuh, Shiva or Ifrit. Don't panic when you don't find them (I did, and I searched for them like crazy). For them to re-appear on the Coliseum I believe you need to make sure you also finished all the interventions and then you need to beat the "true ending" bosses once. The trohpy for the true ending won't pop, but don't panic again. The "true ending" trophy won't pop unless you 1) finished all the interventions and 2) have captured the 7 of the Pleiad.
Then to post-game, to grind levels go to EX Dungeon Z and reach the last room where you find a save point and the purple crystal to teleport to the final boss XG. Equip EXP Boost Mirajewels, use the same 6-team to keep the damage steady and keep switching out the 6 other mirages at the save point when you are able to master the board of one. There are about 200 mirages and you basically need to level up all of them except 5-10 to be able to get the trophy for mastering 100 mirage boards. After level +80 you should be able to oneshot most of enemies in the area. Just the Behemoth stack and the Buer will need few extra hits.
When you are collecting the last mirages from the Coliseum, you will probably be missing 2 of them atleast - Ultima Weapon and Master Tonberry. The most easy way to get them is to level up Bahamut* around level 60 and use it in combat. Summon the mega mirage, leave it to 1AP and low HP and use megaflare. It should take 1/2 of their HP and you should be able to catch them easy. If you overlevel Bahamut* to 80+ it may prove tricky to find the balance between dealing enough damage and just 1 shotting them.
If you're missing more, just check what's the condition to trigger the capture and check which mirages inflict the condition if necessary - Evasion down, Defense down, etc. Oh, and if you're missing the Master Cactuar it's pretty much impossible to hit him with attacks - most if not all will miss. Sleep him first. Then everything works. Stonks.
Find some good series/documentaries on Netflix, HBO, Hulu, YouTube, whatever streaming service of your choice. The grind to mastering the 100 mirage boards will be tedious.
As for my stack setups I pretty much used the same for the whole game (I doub't its very optimized, but it works). Bablizz/Reynn/Behemoth, Tama/Lann/Red Dragon. Strong physical damage, one was focused in water/ice attacks, the other in fire attacks. Put Bashinra in both boards (it will be very very useful), some healing and you're good to go. Use the defense action to restore AP quicker and protect your stacks from breaking.
Cheers and good luck with the platinum!
