Tarsila is one of the World Bosses available in Lost Ark. The boss has more than 10 million hit points and is level 17, killing it will also grant you an entry in your adventurer's note on top of the money and gear it loots.
Even if a boss is not available right when you're in the area you might want to check the area chat as the boss could be available in an other channel.
To change channels, simply click on the CH in the top right corner of the screen and select the channel you want to join.
Where to Find Tarsila in Lost Ark
Tarsila is quite easy to find once you get to the Lake Eternity in Shushire.
