The final request of a dying teenager changed the finale of Breaking Bad.  

Kevin Cordasco had been diagnosed with a rare form of brain cancer, and was a big fan of the show. Creator Vince Gilligan and star Bryan Cranston visited Kevin at his home in L.A., and the one thing Kevin wanted to know was what happened to the Elliot and Gretchen characters who had appeared in earlier episodes. Because of that Gilligan brought them back for the final two shows.  
Gilligan had also asked Kevin if he wanted to know how the show would end, but the teen said he wanted to watch it with everyone else. 
Kevin died in March before the final episodes aired.
--Rob Archer