Downloaded Hydra Slayer quite a time ago, but started playing just recently. Now I see that it's rare fusion of dungeon crawl and maths, and oddly enough it works. Reminds me about one game which is not roguelike but still is turnbased and has twisted puzzles, and that game (or rather series) is DROD - Deadly Rooms of Death. Roaches are not hydras, of course, but are nonetheless challenging to defeat. And then, there are goblins and snakes and bats and growing goo...

But enough of introductions, 'cause I went here to speak about maths!

So, line of Divisors only goes one side (leaving Null Sector alone) - increase of denominators: 1/1 -> 1/2 -> 1/3 -> ... But what about other fractions? The least thing to implement should be

Sesquisector and Quasquisector, these should change quantity of heads by 2/3 and 4/5 correspondingly. They can be displayed as /1.5 and /1.25 [or 2/3 and 4/5, or /(3/2) and /(5/4), or //3 and ////5...], and they will progress with Big Stick as following: 4/5 -> 4/6 = 2/3 -> 2/4 = 1/2, which stands for normal Bisector.

More fun will be going into full forest of fractions, with unholy spawn of (7/3)-Sector turning into good old Trisector after bigsticking it twice. But this will take too much to implement, I think. And names will be too ridiculous.

Also,

reminder that hydras weren't holding the monopoly on multiple heads in Greek mythology. Maybe, that will inspire some idea too.

Once again, thanks for such an interesting expirience of roguelike!