Having grown tired of seeing ponies worship the very ground that the Princesses walk on, Discord decides that it's high time ponies started worshiping him instead.
Ponies, assorted whatevers, We're gathered here today... For the most insane and explosive wedding you have ever seen! Know Your Mare crunched up into one single blown-out wedding!
Finding another that is like yourself (be it personality, interests, species or otherwise) is always a good thing to find. For Discord, however, it's an...experience, of sorts.