Diggi is another version of "digga", which can be either used as an alternative to bro/dude/mate or to express how you feel about the current situation. Diggi is often used by soft/wholesome/cute people.
Diggi i fucking love you
Something that is equally epic or legendary to PewDiePie because pewds is a legend. Sub to him, please!
This is LegenDiePie!
This guy is LegenDiePie!