What is the literary device used in Act 1, Scene 2?

When Hamlet speaks to his stepfather and uncle, the new king, he employs a pun to indicate his displeasure at the king's quick marriage to Hamlet's mother after his brother, Hamlet's father's, death. King Claudius asks why the clouds still hang upon Hamlet, referencing his sadness and continued mourning. Hamlet replies that he is "too much in the sun," where "sun" is a pun on the words "son" and "sun"; he matches the king's metaphor having to do with clouds with "sun," but he also implies that he is "son" too many times now that he is both his father's and mother's son as well as his uncle/stepfather's (1.2.69).  

Hamlet also employs an allusion to the Garden of Eden when he describes life as an "unweeded garden / That grows to seed. Things rank and gross in nature / possess it merely" (1.2.139-141). This reference alludes to the Garden of Eden, or Paradise, after the fall of Adam and Eve. Once God banishes them from the garden because they have disobeyed him, it is no longer a paradise. Nothing good seems left to Hamlet now that his father is gone and his mother, he feels, has betrayed his father. His innocence seems to be lost, just as innocence was lost in the Garden of Eden when Eve ate from the tree of the knowledge of good and evil. Like Eve, Hamlet now believes that he knows evil.

He employs another allusion, this time to Greek mythology, when he compares his mother to Niobe, a woman who so grieved the loss of her children that she could not stop crying. Hamlet says that "[Gertrude] followed [his] poor father's body, / Like Niobe, all tears [...]" and yet, now, just a short time later, she seems fine and happy with her new husband (1.2.152-153). He points out his mother's hypocrisy, or, perhaps, her lack of true feelings by suggesting that she seemed like Niobe then, but is miraculously fine now.