What literary device is romeo using here?
mis-shapen chaos of well-seeming forms!
feather of lead, bright smoke, cold fire, sick health!
still-waking sleep, that is not what it is!
this love feel i, that feel no love in this. (i. i. 167-170)
irony
foreshadowing
oxymoron
allusion

Oxymoron is the literary device used by Romeo in the above passage.

Oxymoron is combining at least two words which are opposite in meaning and ideas to create an effect.

Misshapen chaos and well-seeming forms
feather of lead
bright smoke
cold fire
sick health
still-waking sleep

These are the words that have opposite meanings but give a bigger impact when put together in a literary form.