Rustage songs you should check out:
Eren rap eyes on me ft. Mcgwire
Alucard rap blood ft. Tophamhatkyo
Gojo Running in blind ft. Mcgwire
Makima rap command ft. Saa
Death Note Light Yagami rap fear my touch ft. Mcgwire
Toji rap going for the kill ft. Enpii
Mahito rap pull you down
Someone can correct me if I am wrong, Rustage usually does his own instrumentals, but when he needs more heavier metal instrumentals he gets someone to do it. Nonetheless, he does sound real good on it.
Also if you haven't checked out HalaCG's songs, they are pretty good! I like her Gambler song.
Pretty sure Rustage said he's not good with guitar. So having another person do some crazy electric guitar really elevated this song
If you're more into metal and want to do more Nerdcore things, Fabvl is very very good
!sr THE AMAZING DIGITAL CIRCUS EPISODE 2 SONG "Goodbye" - FabvL
I know Jonathan recently has done a lot of the very low type of vocals on his channel, but he has an incredible range. Especially if you listen to his song "Pesticide" for example, he shows more of his range there (though, to be fair, in a not-so-serious manner).