One thing I love to do is give them itty bitty details that'll annoy the Hell out of you if you're next to a character that they're too stubborn to change. Like them chewing loudly or pronouncing a word a certain way. Makes the other characters go "W-why do you do that? Can you stop that?". :v
As for BIG flaws, I think if the writer is trying to make a story in general well... I think people should probably read-up on figures in history who've done horrible things but end up being forgiven on a mass scale? Just so it can add perspective and make certain redemption arcs realistic. They exist, trust me, and they're probably the most fascinating people imo.
I think when redeeming a character the thing you need to keep in mind is that there IS no one way in doing it (unless you're proving a point). You gotta keep people on their feet and that means redeeming characters in all sorts of ways. For example; a horrible character might end up turning into a goody-goody and that's okay. Because that character came to terms with his flaws and solved it HIS way. Individuality is key.
I think another thing I love is how a character is just like "I accept that I'm flawed... I'm not going to CHANGE it... but still". Either way, give the audience variety.
Honestly for my stories I try to weave the unapologetically crazy characters into my narrative? Like how in That Stick Figure Isekai, the Hand Arc is Naota getting #metoo'd for analyzing potential "girlfriends" by writing down their attributes like friggin' race horses (he kept record of their bathroom schedules ._.). He outright thinks he can get away with it since he's a harem character and disregards the stick figure girl's personal rights because they're nothing more than stick figures. The whole point of the arc was to show that the character that I made the audience cheer for is EXACTLY like the antagonist and the jokes the audience playfully laughed at earlier were red flags for this very moment (a play on the harem genre). It was like a little test. Would they raise their eyebrows or would they come to embrace this character simply because the narrative asked you to?
That said, I want to stress... there's nothing wrong with perfect characters. (Big Classic Superman/Giorno fan incoming :v) I've been hearing statements that they're boring and while I can see where they're coming from, I don't think there's anything wrong with leaning on that if you don't feel comfortable with writing flawed characters UNLESS (and this is a big unless) you're making a point or you have some direction that'll make people on board. In fact, you can make it to the point where they're so perfect it's comical.
I haven't introduced them yet, but there's characters in my story that... doesn't have any particular flaws. They're a huge contrast from the rest of the cast.
Those are my thoughts tho.
@darthmongoose I think with Last of Us 2, I would've loved the faceless other concept (I'm obsessed with that concept)... hadn't been for Ellie killing that pregnant lady. I remember Matthewmatosis making a comment where he's killing random people and was like "Well what if this random lady was pregnant?" or "this guy was close to finding the cure?". Comments like that. I get that's supposed to be the point, but you kill an ungodly amount of people up from what I recall. Like sure, the Uncharted games were comically bad with this.... but and I can't lie... it makes the games even more hilarious lol. I think Playstation All-Stars Battle Royale (which is canon now) made me appreciate it more where Nathan's arcade opening and outro playout like his games but in between... the gameplay... you're fighting raccoons... robots... dog rappers. In the end he casually calls them "freaks" which makes it funnier, but that's about it when explaining what happened. To Sully it seemed like another day (honestly, I hope they keep this as a running gag). Kinda like Yakuza. I WILL say if you like the different perspectives, Hotline Miami is a fascinating take on it. The way they transition between the two storylines made my eyes pop-out. I was like "WAIT. THAT'S NOT HOW THE NARRATIVE WAS SUPPOSED TO PLAY OUT" (Hotline Miami 2 is a little more risky with its content). No More Heroes has the same themes as Last of Us 2 (even uses animal symbolism, but the protagonist is outright a metaphor for juvenile teenage male players). It's cool seeing how Ellie and Travis end up in the same situation and how they deal with it.