I'd like the ability to add and view video and blog links when at an individual puzzle's page.

Import from a strictly-formatted CSV, with minimum of fuzzy-matching on name of puzzle, and suggested further matching on metadata of designer, producer, etc. This will better help match to the correct puzzle. You'll get a "best guess" of top 3 that match your puzzle, and you can choose the best one that represents your collection. If none match, you can search by keyword manually for a match (sometimes under a different name or producer), or an "add as new entry" toggle to create a new page instead for said puzzle upon import completion For large collections, this would be best to do in chunks of 50, that way a substantial state doesn't have to be held and potentially lost, and processing happens in segments

Today, we can only add in collection or mark as solved, but can't remove from collection or mark as unsolved (in case it was marked accidentally)

When looking at auction results on a puzzle, a way to flag a connection as wrong, preferably with a few quick "why is this wrong" checkboxes and a text field for a quick explanation. for more UI space or complexity (you masochist) you could allow the user to optionally search for and select a puzzle they think would be the right option instead.