After announcing the Monster Hunter World: Iceborne and Witcher 3 collaboration, there are 2 new events that were not mentioned and one of the events is currently live. Quest name “SDF: Silent, Deadly, and Fierce” fight Odogaron, Deviljho, and Lunastra in the arena and the rewards include layered armour and armour sets from Assassin’s Creed.
The second event appears on the official Monster Hunter World website under the event page. There is one event showing “???” and is available only on 31st Dec until January 1st 2019, the event is most likely related to the New Year, so let’s see what Capcom has up their sleeves.