Plot hole: At the end, everyone was returned to their own timeline. Except for Ted's dad. He's shown still playing till the end and not disappearing like the others. However, this version of Ted's dad came from the future when he attempted to arrest his son at David Grohl's house. Therefore, he should have disappeared with the others and returned to his future timeline.
Suggested correction: That's not what happened at the end at all. Only those whose were time-displaced returned to their own timeline. Which is why we see Kid Cudi leave, he was time-displaced and not picked up in the time machine. You can even see Ling Lun is still playing.
Incorrect. Ted's dad was time displaced as well. He never arrived by the time machine, but was sent to hell after being killed by Dennis. Therefore, he should have been sent back to his future timeline.
Ted's dad was never time-displaced, nor did I say he arrived by time-machine. He was sent to Hell in his own time line and then went with the group to 2020. Unlike Kid Cudi who was time-displaced because he popped out of his own timeline because of time and space collapsing. Just being from a different time isn't what time-displaced meant.