I completed True Pacifist...

Spoiler:
I accidentally spoiled for myself that Flowey was Asriel. I DIDN'T know a thing about Chara though... Honestly I didn't really want to do a genocide run so I just read about it. XD I now understand the "plan" that was mentioned in the VHS tapes... So twisted! Chara is messed up. xD

Also I didn't know that the fish place in Waterfall was Undyne's house, so I never had the Undyne friendship arc or access to Alphys' True Lab in my first (neutral) playthrough! Meaning that I completed all that this time around, which was a great time to do it. XD I'm glad I kept it for this playthrough so it was something new and a little different. :3 Because I was rather disappointed that I didn't get to spend time with the characters outside of what was practically the first half of the game. Sans and Papyrus (Papyrus especially) sorta vanished after Snowdin so I was glad to see that there was a bit more character interaction. And for Undyne! I really wanted to get to know her and like her. However, with what little you have to work with if you don't befriend her, it's hard to gauge her character at all. Lel. So yeah, I'm happy with the extra stuff--especially the True Lab! o.o Wtf. So interesting.

The final fight with Asriel was really cool. I liked hearing about his story. I feel so bad for him. :C Stupid Chara, getting him killed. What a buttpie. But yeah, I also love the little details that you'd only notice after completing the game and going back... Because they're allusions to what you learn.