Steven Universe: Unleash the Light

The Black Hole dungeon consists of randomized stages (between 3 and 6, depending on the difficulty), a cosmic treasure chest, and a boss fight.  It may also contain regular treasure chests and shop stages, but that's not always guaranteed.  The bad news is that if your entire party dies, all of your progress on your current run is wiped out and an entirely new run is generated.  The good news is that you can close out of the game and come back to the same run, meaning that you should be backing up your save between stages - especially on your Crying Breakfast Friend run.

Other than enemy HP and strength, there are different rules based on what difficulty you're playing:

Normal: N/A
Hard: Your cheeseburger backpack is empty.  You can only use items that you've picked up while playing in the dungeon.  Hopefully you get good shop spawns and can just revisit them to pick up things like star fruit, Rose's tears, etc.
Diamond: Your cheeseburger backpack is empty.  Additionally, the purple QTE star that allows you to get perfect hits/blocks is absent (the yellow one is still present, so there's still some help in timing it)

Do note that you only have to complete each difficulty once - which just entails defeating the boss - so defeat the boss as soon as you get access to it.  It does not necessarily come after the final numbered stage!  I had a run on hard difficulty (5 stages) where I could access the boss fight after stage 2.  This is also why you should be farming keys on normal difficulty.  The cosmic chest is not required for completion but IS required for Perfect Porkchop , so try to open the chest, even on your run for this trophy.

You need to 100% these stages for Perfect Porkchop .  The way to 100% the stages is to open four cosmic chests on each difficulty - outside of the one time you need to fight a boss on each difficulty, all you need to do is progress far enough to open the cosmic chest.  Farm cosmic keys on Normal difficulty (they are almost always somewhere in the third stage - look for the question mark icon on the map).  The cosmic keys will carry over between difficulties.  So find all eight keys you need for the higher difficulty chests, open the cosmic chest in each run, then hit the reset button at the top of the map or die - you'll still keep the chest opened count/completion percentage (thanks to Bdemonkid666 for confirming).

There are some unique items you can get from the cosmic chests, but all that's required is to just open them four times.  The unique items: Onion's Badge, the Prism Pal Badge, the Rose's Tear Badge, the Ambidextrous Badge, and Connie's two costume schematics.

There is a party you can put together that will allow you to fly through enemy encounters. This strategy hinges on how you upgrade Amethyst.

Equip her with the Lucky Star Badge (should be in a chest after the world 3 boss fight) and Shamrock Badge (should be in a chest on the balcony of Palace of Light).  Craft her alternate costumes so you can equip the Super Star Whip perk, and make sure that perk is equipped.

In terms of her upgrades, you will want to have the Lucky Star, Whiplash, and Show Off upgrades unlocked.  This will take a total of 34 skill points (Amethyst will need to be around level 25), so you may have to use a redo idol to reset whatever upgrades you've given her so you can reallocate those points.  You can still do this without Whiplash, which will save you several points; Whiplash just makes this easier.

Setting up Amethyst this way, combined with how you time her whip hits, will usually generate an unlimited amount of star points, meaning that you'll often just kill all enemies before you even need to end your turn.  This is most obvious and effective with enemy groups of at least three or four; with smaller groups you may want to default to Garnet, to make the best use of your star points per round.

Team formation:
Amethyst in the back - equip her as stated above
Garnet in front - Lucky Restore and Frontline badges
Steven and Bismuth at top and bottom - put whatever you want on them based on your play style - if you're on your Crying Breakfast Friend run, one of them will be wearing that badge.  Make sure Steven has the perk that allows him to use the cheeseburger bag twice in a single round, and ideally, unlock the upgrade that allows you to access the backpack even if Steven has fallen.

If you're on your Crying Breakfast Friend run, this strategy won't work as well, but it still works on larger groups of enemies - it just takes longer to get started.