Understatement,Oxymoron,Periphrasis and Hyperbole.

Understatement is a figure of speech in which a writer or speaker deliberately makes a situation seem less important or serious than it is. F.e:It's just a scratch. Hyperbole is  an extreme exaggeration used to make a point. It is like the opposite of “understatement. F.e: I’ve told you a million times. Oxymoron is a figure of speech in which incongruous or seemingly contradictory terms appear side by side. F.e:This was a minor crisis and the only choice was to drop the product line. Periphrasis is a device by which grammatical meaning is expressed by one or more free morphemes instead of by inflectional affixes or derivation. F.e:The king of the football team hiked the ball.