What are the different ways rappers can bend vowel sounds?

General thoughts

• You can use this chart as a guide for the kinds of substitutions that might be less noticeable / obtrusive to the listener: https://www.ipachart.com/
  • 
  • The idea being that the closer that two vowel sounds are on the chart, the less noticeable it may be to substitute one for another.

Common

• -er to -uh
  • IPA: ɚ to ə
  • Example words
    • paper to paypuh (Source)
    • neighbor to neigh-buh (Source)
  • Example artists
    • Notorious BIG uses this heavily.
  • Thoughts:
    • This might not actually be a bending of the vowel sound, it might just be a dropping of the 'r' sound.
• -ar to -aw
  
  • IPA: ɑɹ to ɔ
  • Example words
    • barbershop to bawbuhshop (Source)
• -awr to -uh
  • IPA: ɔɹ to ə
  • Example words
    • corridor to corriduh (Source)
• -ing to -in
  • IPA: ɪŋ to ɪn (Sound guide)
  • Example words
    • seeing to seein'
  • Thoughts
    • Interestingly, at least with Americans this is only for the '-ing' ending, rather than for any 'ng' ending.  So, for example, you don't hear Americans changing 'bang' to 'ban'.
• -and to -in or -n
  • IPA: ænd / ɛnd to ɪn
  • Example words:
    • and to in or 'n
    • thousand to thow-zin' or thouzan'
• th to t
  
  • Example words
    • with to wit
  • Example artists
    • Notorious BIG
• th to d
  
  • Example words
    • them to dem
  • Example artists
    • ...

Uncommon

• -uh to -aw
  • IPA: ə to ɑ (Sound guide)
  • Example words
    • cham-pee-uhn to cham-pee-awn
    • eye-ver-suhn to eye-ver-sawn
  • Example artists
    • Asher Roth does this for two words in his song I Love College