It's always nice to see tricks. 

Some time ago I did a Ruby Tips and Tricks presentation, maybe it can give you more ideas for the part II.

http://www.slideshare.net/Scudelletti/ruby-tips-andtricks

About `fetch` you can also pass the default value as the second argument instead of a block.
`{a: 1}.fetch(:b, 200)`

Nice video!