Voice effect

Hi all, watch this from 3:10 and tell me what effect is there in his voice!

I dunno but what about first normal singing, then a little falsetto and after that it sounds like slide guitar to me?
Going via falsetto to slide seems like a deliberate attempt to make a seamless transition to the slide.
I can be wrong but no matter what it sounds really cool.

it’s just a super distorted/saturated voice layered with dist.lead gt (not much to do about voice fx in 90s)