All 6 Uses of

grotesque
in
The Great Gatsby

This is a valley of ashes — a fantastic farm where ashes grow like wheat into ridges and hills and grotesque gardens; where ashes take the forms of houses and chimneys and rising smoke and, finally, with a transcendent effort, of men who move dimly and already crumbling through the powdery air.
p. 23.3 *

grotesque = distorted

The most grotesque and fantastic conceits haunted him in his bed at night.
p. 99.0

I Couldn't sleep all night; a fog-horn was groaning incessantly on the Sound, and I tossed half-sick between grotesque reality and savage, frightening dreams.
p. 147.1

grotesque = distorted and ugly

...as he found what a grotesque thing a rose is...
p. 161.6

grotesque = distorted in a disturbing way (from what was imagined)

Most of those reports were a nightmare — grotesque, circumstantial, eager, and untrue.
p. 163.6

grotesque = distorted and ugly

I see it as a night scene by El Greco: a hundred houses, at once conventional and grotesque, crouching under a sullen, overhanging sky and a lustreless moon.
p. 176.6

grotesque = distorted in an unnatural way

Definitions:

(1) (grotesque)
distorted and unnatural in shape or size -- especially in a disturbing way

or:

ugly, gross, or very wrong
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

More rarely, grotesque can refer to a style of art or instances of it that combines or distorts in a fanciful way natural forms into something that is often ugly or disturbing. Grotesque can also be used specifically to reference a gargoyle-like sculpture without a waterspout.