This is the 16002nd most frequent Polish word.
trudnego
"Trudnego" means "difficult" or "hard" in English (genitive or accusative singular form of "trudny").
Here, 'trudnego' is used as an adjective in the genitive case describing the noun 'charakteru' (character).
Zadanie było trudnego charakteru.
The task was of a difficult nature.
In this sentence, 'trudnego' functions as an adjective describing 'czymś' (something) and is in the genitive case due to the construction following 'czymś'.
Spotkałem się z czymś trudnego do zrozumienia.
I encountered something difficult to understand.
Here, 'trudnego' modifies 'niczego' (nothing) and is in the genitive case, aligning with the negative construction.