This involves doing the field bosses in the lower level areas for;
Rudric - Rethramis Border, Rethramis
Salt Giant - Saland Hill, Yudia
Roblom - Bilbrin Forest, West Luterra
Wili-wili - Sunbright Hill, East Luterra
Caspiel - Skyreach Steppe, Tortoyk
Highly recommend using
https://lostarkmap.com for map locations.