Words like 'resilient', 'placid', and 'furtive' are useful. 'Resilient' is great for characters who can bounce back from difficulties, like a resilient orphan. 'Placid' can describe a calm setting, for example, a placid lake. 'Furtive' is good for creating a sense of secrecy, such as a furtive glance between two characters who are up to no good.
Some good words are 'gloomy', 'ebullient', and 'enigmatic'. 'Gloomy' can set a dark or sad mood, such as a gloomy old house. 'Ebullient' describes someone full of energy and enthusiasm, like an ebullient young hero. 'Enigmatic' makes a character or situation mysterious, as an enigmatic stranger who arrives in town with a secret past.
Words like 'magnificent', 'serendipity', and 'whimsical' are great. 'Magnificent' can be used to describe grand things like a magnificent castle. 'Serendipity' is perfect for when unexpected but pleasant things happen in the story, for example, the characters discover a hidden treasure by serendipity. 'Whimsical' is good for adding a touch of fancy, like a whimsical forest full of strange and wonderful creatures.