who is the elf lady and how do they know her?
That's Katie Marovich, who has been a writer for Dropout since it was CollegeHumor. She's easily one of the funniest people they employ.
Edit to add: one of Droput's MOs is to piss Brennan off. Sam Reich does everything in his little mischievous power to get a rise out of that poor, poor man.
Personally I don't like watching liveplay ttrpg shows, so my favorites to watch are Gamechanger and Make Some Noise. I also love Smartpants and Gastronauts, and occasionally we'll catch Um, Actually.