This is from what ive found out so far. Will be updated ASAP. Feel free to correct me.
New Items:
New Items available from Tailoring/Blacksmithing.
New HAndicraft items?
New Content:
Marriage System with new clothes for that.
Upgraded Pet System/AI.
Skills:
Skill Cap Removal.
Secondary Hotbar.
Dark Knight Transformation/Skills.
Cash Shop:
More Premium Character Card options.
G3 Mainstream, Dark Knight.
New Pets.
G3 Trailer
Mabinogi Video