Intervention - S4-E4
Revealing mistake: In the flashback when Ted damages the ceiling beam with the flail, you can see that the damage is already there before Ted actually hits it.
Intervention - S4-E4
Revealing mistake: When the encyclopaedia bookshelf falls off the wall in the flashback, you can see the wall being pushed out, showing that it was being manipulated from the other side by crew.
Chosen answer: In a flash forward scene in Season 8, it shows him with his first born: a daughter.
XIII