Ultimate Custom Night

The way I got all of the jumpscares from the main set of 50, was by setting everyone to 50/20, starting a game, and then getting jumpscared. Whoever jumpscared me, I would set back to 0, and go back in. Eventually you'll be left with a few, that you might have to trigger a little. Some will only attack after you've gone in the monitors. It's easy enough to read how to block them and do the absolute opposite.

This leaves DeeDee's animatronics. She can summon a handful but there's only three with actual jumpscares that can kill you, the rest just inconvenience you. You're looking out for:
-Plushtrap
-Nightmare Chica
-Bonnet

Plushtrap will appear on Funtime Foxy's camera, sat in his chair. You watch him to make him go away. Of course, you don't want to do that, you want him to attack, so just ignore him.

Nightmare Chica will be immediately apparent. Her jaws will begin to cover the screen. Just let her chomp you.

Bonnet will giggle and run through the office, let her do that and the jumpscare is yours.

What's nice about these DeeDee animatronics is none of them have death dialogues, so if you are aiming for the other achievements, you don't have to worry about summoning them.
Because summoning them is really hard. I tried different strategies, including doing a night of only animatronics that can't kill you on 20, so I could idle the game. She just wouldn't show up. It sucks.

There's not really good information on how long she takes to trigger, I've read 45 seconds. I feel like the animatronics might impact it but I really don't know. The only advice I can give for triggering her is just to continue going for the other achievements, and if she spawns, try really hard to get jumpscared by the new animatronic and pray its a new one. You'll be playing with a 1/56 at worst, and that chance will get higher the more animatronics you play against.

EDIT: I've found a good strategy for getting DeeDee.

Set the game to 50/1 mode. Every animatronic on 1. At this point, they'll be tolerable enough for you to last long enough to get DeeDee.

Play until 45 seconds. Your main focuses should be setting a vent block, duct lure, toy freddy, checking on FT. Foxy to make sure he isn't at 1am, turn your fan off, keep an eye on the right hall for the plushie animatronics, and close your door when you lift the camera up when the office heats up (Freddy will approach faster)

Also, set the GMB on, that'll eliminate Chica, Lefty and Puppet. Don't check Chica's camera, for some reason that just aggros her.

It's kind of learning through failure, keep trying and when you die to an animatronic, keep an extra eye on them and you'll get used to it.

You want to get to 45 seconds, as DeeDee has a chance to spawn then. If she doesn't, quit (or die to an easy animatronic) and try again.

If she does spawn, great! Let her do her song. As soon as she appears I'd shut everything and try to eliminate as many animatronics as possible from getting me, fan back on, etc.
If the NEW CHALLENGER text appears, great. Just survive long enough to see who it is, and it'll be someone new because everyone is active at 1. If no text appears, she bumped someone's AI up, quit, lower them back down, and try again. Happy hunting, fellas.

As stated, for this achievement you must be jumpscared by everybody.(This will be updated once I can confirm them all)

Need:
-Freddy
-Chica
-Foxy
-Toy Freddy
-Toy Bonnie
-Toy Chica
-Mangle
-Withered Chica
-Withered Bonnie
-Puppet/Marionette
-(Withered)Golden Freddy
-Springtrap
-Nightmare Freddy
-Nightmare Bonnie
-Nightmare Fredbear
-Nightmare
-Jack-O-Chica
-Nightmare Mangle
-Nightmarionne
-Nightmare BB
-Circus Baby
-Ballora
-Funtime Foxy
-Ennard
-Happy Frog
-Mr. Hippo
-Pigppatch
-Nedd Beard
-Orville Elephant
-Rockstar Freddy
-Rockstar Bonnie
-Rockstar Chica
-Rockstar Foxy
-Musicman
-Molten Freddy
-Scrap Baby
-William Afton
-LEFTE
DD Character List:
-Plushtrap
-Nightmare Chica
-Bonnet

Not 100% sure yet(will update later):
-Bonnie
-BB
-JJ
-Phantom Mangle
-Phantom Freddy
-Phantom BB
-Old Man Consequences
-Trash and gang
-HELPY
-El Chip
-Funtime Chica
-Phone Guy
DD Character List:
-RWQFSFASXC
-Minireenas
-LOLBIT
-Fredbear