rhyming most emcees do one or the other to the extreme and im not saying eminem started this or he is the only one that does but eminem to me took it to another level.
example
And they say that love is powerful as cough syrup in Styrofoam
All I know is I fell asleep and woke up in that Monte Carlo
assonance to me is just another verison of slant rhyming expect unlike slant rhyming u don't need the consonants
u just need the syllable sound as long as phonetically match it is considered a rhyme now eminem does that but also mixes it with perfect rhyming pretty genius if u ask me imo