I'm sure people would like to know how many kats there are on the various levels. I counted the kats in Grim Gallery and found 35 (1 of which was a Black Kat). Is that good/bad compared to candlestick keep?
Kats on static levels:
Grim Gallery: 35
Cravat Hall III: 30
most lvls have fixed ammount of monsters ;)
for candlestick i think it's the same but you also have to take into account that the maps are random so some maps have more/less cats and more zombies for example. for the clockwork tunnels i have no idea if the number is random or if the spawns are fixed (i think random)
Black kats have a small chance of spawning randomly wherever there would be a normal kat. Therefore levels with more kats have a higher chance of spawning a Black Kat (or more than 1). The dynamically generated levels have a random number of monsters and therefore kats (in the case of Candlestick Keep, in my experience around 15). The static levels have a static number of monsters, and I think in the case of the Scarlet Fortress series, more than Candlestick Keep.
they spawn randomly, there is no way to get the overall chance.