A Pony usually becomes Discorded when they lose faith in their best traits. They will lose their bright hues and become more and more grayscale the more they lose faith. It is currently unknown what will happen to a pony if it loses all faith whatsoever.
Ponies Who Have Been Discorded
When a Pony becomes discorded, they usually express the opposite of their greatest trait.
Captain Jack Harkness: Destroyed Torchwood and insulted the Doctor and his allies. Became really bad and lost everything in his life. He became Unfaithful, lost hope in friendship, became lonely and was friendless.
Applejack - Lied and was never Honest. She was insulting her friends.
Rarity - Was Greedy and stole stuff. She wants things that she wants. She also became rude.
Fluttershy - Was Cruel and Mean and Firm at her animals.
Twilight Sparkle - Lost hope in Friendship and never trusted her friends.
Rainbow Dash - Left her friends and Betrayed them. Being rude to her friends.
Pinkie Pie - Became suspicious of her friends and really Sad and Angry.
Moon Drop - Became scared of everything, became nervous and shy.
Coma Surge - Became idiotic and became really stupid.
Princess Holly - Disappeared and ran away.
Princess Pepper - Lost hope and never trusted anyone.
Catliyn - Became moody and always being angry.
Tamara - Lost sense
Brooke - Lost drive
Cheryl - Greedy and was really not generous.
Clarrisa - Was mean and selfish.
Lush Denim- Became Friendless and lost hope in friendship.
Crystal Treetop- Was Selfish and cruel
Ricardica- Was Pessimistic and was worried.
Twister Torso- Was a scaredy cat