As far as I've been able to see, the basement content for 0.3.5 is:
(spoilers)
Gang route:
after delivering Davide's packages 5-6 times talk to Davide at 9pm
Basement tour and meeting new blonde woman
MC + Davide spit-roast blonde in stocks
Mom arrives. If relationship is 6 or less then you have the following options
- Davide fucks mom while you fuck the blonde in ass or pussy
- Davide fucks mom while you just watch
- You spank mom while Davide fucks the blonde
If your relationship is over 6 then you can only spank mom while Davide fucks the blonde
This is all the the basement content for the gang route
Sister route:
after going on date with little sister you have the option to explore the basement from your room at any time
Look around the basement, and then someone comes in
If relationship is less than 6 and you met with Davide during Little Sister's date
Davide enters and you have the following options
- Davide and Little sister talk/flirt while you remain hidden. She looks at and touches Davide's cock a little
- Davide and Little sister talk/flirt in front of you
- You get angry at Davide for talking to your sister
If your relationship is over 6
Mom enters and plays with a sybian. You have the following options
- Grope/finger little sister while listening to mom
- make out with little sister while listening to mom
This is all the basement content for the sister route.
Currently you can do both routes in the same playthrough, and every time you enter you get the same choices.