Hi, I'm asking here in case someone knows a bit about this.

I would like some advice about how to add some special voices or effects for the vocals in songs, I mean, there are the main vocals but I would like to add some effects at some points in the songs to bring a more evil feeling.
is there some particular tools to add such things, recommended? Anyway, if you guys have some tips, let me know, thanks.

Reverb and Delay are the salt and pepper of vocal effects. I would start there.

You can play with a chorus effect, some warm tube distortion or even, if you dare, experiment with a bit-crusher.