I played 100 games in standard Ascension 100+ and recorded how many of each demon and minion appears.
Minion: 24%
Twin Minion: 13%
Witch: 21%
Shaman: 12%
Poisoner: 18%
Chancellor: 35%
Puppeteer: 17%
Puppet: 16%
Baa: 33%
Pooka: 33%
Lilis: 34%
Chancellor and Witch are over-represented while Shaman is under represented.
I also broke down how often each minion appears with a particular demon
Minion with Baa: 4/33 12%
Twin Minion with Baa: 4/33 12%
Witch with Baa: 10/33 30%
Shaman with Baa: 4/33 12%
Poisoner with Baa: 4/33 12%
Chancellor with Baa: 12/33 36%
Puppeteer with Baa: 5/33 15%
Puppet with Baa: 5/33 15%
Minion with Pooka: 16/33 48%
Twin Minion with Pooka: 4/33 12%
Witch with Pooka: 5/33 15%
Shaman with Pooka: 4/33 12%
Poisoner with Pooka: 2/33 6%
Chancellor with Pooka: 8/33 24%
Puppeteer with Pooka: 1/33 3%
Puppet with Pooka: 1/33 3%
Minion with Lilis: 4/34 12%
Twin Minion with Lilis: 5/34 15%
Witch with Lilis: 6/34 18%
Shaman with Lilis: 4/34 12%
Poisoner with Lilis: 12/34 35%
Chancellor with Lilis: 15/34 44%
Puppeteer with Lilis: 11/34 32%
Puppet with Lilis: 10/34 29%
Pooka, Lilis, and Baa were evenly balanced at 1/3rd each.
Chancellor, Minion, and to a lesser degree Witch were more likely to be a “+1”: appear in games which already had another minion in them, contributing to their frequency. Shaman and Puppeteer/Puppet were more likely than other minions to be the only minion it their round.
Lilis overall had the most minions at 67 in 34 games, followed by Baa at 48 in 33 games, and Pooka had the fewest minions at 41 in 33 games.