This game may be cute and funny, but don't take it too lightly, this RPG probably has the most customization out of all the Compile Heart games since it has a 5 mb save file. Mugen Souls Z has versatile gameplay, so I can't really give any solid tips since there are hundreds of ways to play this but I can help if I can get more information about your situation.
Since you're creative and smart, you can figure out how to get past the obstacles. The JP version of Mugen Souls Z has an 8.32% platinum rate while the EN version only has 1.42%, probably because they're more of a casual RPG gamer who are used to the main story being the bulk of the game while the Japanese are used to RPGs where the story isn't a big part.
Mugen Souls Z takes a lot more thinking than most turn based RPGs. I'm not saying the battles will take thinking, but setting up your characters, finding out the best combinations of equipment, finding out where to find them, examining the enemy's potential, etc will help you get a platinum unlike more other turn-based games which you can win by simple grinding. The better you are at time management and calculating the best method for maximum earnings will drastically shorten the platinum time.
People take the game too lightly and don't take advantage of everything. The main story is a tutorial that's supposed to be cakewalk while the post game and special worlds is how the real game is really meant to be played. The first game's platinum was an extreme test of patience and pain while Mugen Souls Z platinum tests you more about how well you know how well you can work with the game's systems.
I highly recommend getting Self-Defense+100, Gained Mugen Points Up+150%, Gained EXP Up+150%, HP Auto-Restore+25, SP Auto-Restore+25 when you start to feel like using matter. Self Defense+100 helps a ton since that doubles the stats of everything on all 4 of your defense slots.
This is just my overview on the platinum, it's hard but doesn't take very long to get a platinum like how a real platinum should be. If someone says they are a hardcore RPG player and can't get past the post game, they're not taking advantage of all of the resources or they mean that they are hardcore at grinding. RPGs usually have simple platinums by just playing through the game and enjoy the story but this one requires a bit of thinking and doing battles with bosses who destroy unprepared players. Mugen Souls Z has insane numbers and most gamers don't have the mental capacity to calculate all of the variables the game has to determine success or failure. Getting this platinum should be incredibly fun for creative people who enjoy testing best character builds to exploit the enemy's weakness.