Hi Beni.
It's a tricky list... most monsters and encounters have an anal option, as well as followers/lovers/slaves and recurrent characters, and also depends your member, if it's too long/wide some scenes wouldn't be available (and also some chars won't even let you sex them if you have a specific type of tool, I think).
If you want to keep your monster 20" schlong, better get another one, of moderated size (say 12" or less), this will automatically let you sex smaller monsters/characters (even unlocking DP scenes ignoring your first cock's size).
So, best advice, go get another cock, and start the rampage!