The Deadly Vengeance of Deadly Revenge on Varos is the second serial of Season 22.
The Doctor and Peri need some Zeiton-7 (aka. Zyklon-B) to make the TARDIS work again and the only place they can get it is a planet called Varos.
The Doctor gets wrapped up in the local reality TV show where people are tortured and killed for entertainment (much like The X-Factor or American Idol). And we meet Sil for the first time, who is some kind of manlet slug. He shows up again later in Mindwarp.
The Doctor pushes some poor unsuspecting fools into an acid bath and quips "You'll forgive me if I don't join you." He nearly gets lynched at one point, but later gets dubs to make up for it.
Sil was also a great villain. He was probably the only Sixth Doctor villain who did not want to rape Peri. In fact, the prospect of raping Peri would probably horrify Sil more than Peri herself; "Want this I most certainly do not!"