This is the 6261st most frequent Japanese word.
グロテスク
Grotesque; bizarre, unnatural, or distorted.
Here, グロテスク is used metaphorically to express that his speaking manner had an unnatural or unsettling quality.
彼の話し方が少しグロテスクに感じました。
His way of speaking felt a bit grotesque.
In this context, グロテスク emphasizes that the monster's appearance is bizarre and horrifying, fitting a common trope in this genre.
その怪物の姿は映画の中で非常にグロテスクでした。
The appearance of the monster in the movie was exceptionally grotesque.
In this sentence, グロテスク (grotesque) is used as an adjective to describe the painting as disturbing or abnormal in appearance.