How to hide episodes from my to-watch list?

On the Episodes to watch page, by clicking on the three small dots in the bottom right corner of the relevant episode, a menu will appear containing, among other things, the "Don't watch this episode" and "I got this episode" buttons. Click on "Don't watch this episode": it will automatically be hidden from your to-watch list.

On a show's page, the "⋯" menu of each episode in the list offers the same option. On the page of a specific episode, you can also choose not to watch an episode via the "Options" menu.

If these are specials, you can choose to hide them completely in your account settings by unticking "Display the special episodes of the shows I watch".