The 2nd Free Title Update will be coming to Monster Hunter: World on April 19th. The update will include the addition of a new Elder Dragon, Kulve Taroth, and a new map, the Caverns of El Dorado, to hunt Kulve Taroth.
Kulve Taroth is an entirely new giant monster that hasn’t been introduced in the previous titles and has remarkable golden horns and skin. In order to hunt Kulve Taroth, the players will have to go investigate and hunt in the Caverns of El Dorado, where Kulve Taroth’ nest is located.
According to the explanation here, Kulve Taroth is classified as an Elder Dragon, and up to 16 players can gather at the Gathering Hub to take part in the Siege as several hunting squads; during the Siege, they will cooperate with one another to hunt Kulve Taroth. Players can obtain Kulve Taroth materials from the Siege, which they soon will be able to craft armor and weapons with.
The Kulve Taroth Siege will be available starting April 18th, 5:00 PM PST / April 19th 1:00 AM BST when the 2nd update is added and only for a limited time; there will be another opportunity to join the hunt later on, but details on the date have yet to be revealed.