I've solo'd about 30 floors (all Candlestick Keeps and Scarlet Fortresses), and I've found 3 Kats so far. Once was with one party member, Twice solo. I'm wondering, because some people say that they've found Kats on every floor they've tried, which makes me really frustrated considering I can't seem to find any over many hours of trying.
Does party size affect appearances of Black Kats?
No.