This is the hardest trophy in the game. This is a strategy of how to get it.
There is no shortcut but if you approach it as I have, it makes something which seems impossible at first manageable. This is doable and you'll have a sense of achievement when you get it!
You will be getting the following trophies at the same time, and
it is important not to go for them separately in order to make this strategy work:
Note: there is no point in going for this on its own since, unless you won't be going for "You shall not pass," as it stacks. To put it another way, it would be a waste of time.
and
This trophy will also be unlocked as part of "You shall not pass":
So for "Everybody has a chance", you need to beat the final boss with all 4 characters (the 3 regular characters, and the secret white Kroma character which you unlock after beating the final boss, Krogma, the first time). So here's what you do:
1. For the first 3 runs, for which I suggest you use the regular characters (keep track of which you've used!), focus on practicing beating the final boss, Krogma. Practice truly does make perfect, and after grinding the first 3 runs, you will have a pretty good handle on the mechanics of beating him. Take as long as you need, and
focus only on the part after the checkpoint -- there is no need to practice the beginning of the stage.
2. On your 4th run, which if you followed my suggestion will be with the secret white Kroma character which you unlocked after beating the boss the first time, you simply start the level from the beginning every time. To be absolutely certain, I always use "Restart Level" from the menu even if I die on the first part of the level (before the checkpoint). By this step, you should pretty much have the first part of the level memorized and be able to go thru it each and every time without dying, but if not, simply restart the level every time until the first part becomes easy.
3. Just grind away. Because of the experience you've gotten in step 1, this should be relatively easy. For example for me, I almost did it in the 3rd attempt (I came 1 shot short) and was eventually victorious on my 7th run.
EDIT: if you're gonna downvote, consider first asking a question/explain yourself. It took some time & effort to write this. Constructive criticism is welcomed!