Couplet
"Two such opposed kings encamp them still
In man as well as herbs grace and rude will" (I I. iii.58-59).
This Shakespearean Couplet has meter and rhyme.
Allusion
"The numbers that Petrarch flowed in"(II.iiii.41).
This allusion references the poet Petrarch that preceded Shakespeare. Petrarch was famous for his love sonne. ts. Mercutio is referencing this fame to make fun of Romeo's behavior that is very reminiscent of a petrarchian love sonnet.
Simile
"I warrant thee my man's as true as steel" (II.iiii.203).
Romeo uses a simile to convince the nurse that his servant is trustworthy.
People in this time put a lot of trust into thier swords. This is why steel is used in this simile to embody trustworthiness.