note: the words he chose are very historical-drama-like. 몹시 (very) is still commonly used but more as a written form. 크오 (a variation of 크다 (be large)) is exactly what you'd normally (and only) hear in historical dramas (verbs and adjectives ending with -오).

— doolset in 🇰🇷 (@doolsetbangtan) March 17, 2019