I accidentally hit c with a card selected and archived the card. I tried to undo the archive but couldn't find the option. I tried moving the card back to the list but that didn't seem to work.
How to undo card archive on Trello?
trello;trello cards
In the top right select Show menuThen click MoreThen click Archived ItemsYou then click the Send to Board button on the item and it will be reinstated to your board.