This is the twentieth instalment of the Fortnightly Topic Challenge described here, with topics suggested and voted on here. This fortnight's topic is pattern (suggested by BmyGuest), and will span from the the 14th of November to the 27th of November. During this period, we will compile the list of questions with this tag and post it as an answer to this question.
In the meantime, please go and propose and vote on future challenges!
Everyone have fun, and happy puzzling!
Link to other Fortnightly Topic Challenges.