What impact does line 9 have on the tone of the poem?

In line 9, John Donne abruptly changes the sentence structure of the poem, marking the switch away from the imperative that predominates the first eight lines. By inserting a sentence that is primarily a list, with mostly one-syllable words, the speaker emphasizes the numerous things to which Death is a “slave”; by using only one three-syllable word, “desperate,” they draw more attention to that word. The short words and list format act to speed up the pace, which changes the tone to one of impatience and enhances the feeling of an argument rather than a conversation. The characterization of the kind of people Death associates with, “desperate men,” also contrasts markedly with the “best men” the speaker mentioned in line 7, and with the “kings” in line 9. The items in the line also set up an overall change to negative associations, with “poison, war, and sickness” following in line 8.
https://www.poetryfoundation.org/poems/44107/holy-sonnets-death-be-not-proud

"Death, be not proud" is a sonnet, divided between the first eight lines (octet) and the remaining six (sestet). In traditional sonnet form, the octet presents a problem that is resolved in the sestet. The transition from the last line of the octet to the first line of the sestet is called the volta, or turn. This is a shift in the argument or the subject matter of the poem. The ninth line of a traditionally-structured sonnet is therefore pivotal; a problem has been presented and now it's time for a resolution.
In "Death, be not proud" the ninth line is as follows:

Thou art slave to fate, chance, kings, and desperate men,

In this line we can see the speaker's contempt for death increase. There's a greater sense of urgency from now on, a much more vigorous, attacking tone. In the first eight lines, death has been presented in negative terms (not proud, not mighty, not dreadful, etc). But now the speaker tells death not what it isn't, but what it is, and that is a "slave to fate, chance, kings, and desperate men."
https://www.poetryfoundation.org/poems/44107/holy-sonnets-death-be-not-proud