if i understand you correctly , this is doable up to a certain extend as in the following screenshots (not 100% what you are asking, but , as i assume those are just examples, you might find this is actually what you might want/need)

so, for example one (and/or two as they are the same thing really):
1x Small Pizza A 6$
1x Small pizza B 0$ (Free)

you would do this (click for image) in the backend

outcome frontend (click for image)

example 3:
>If a customer chooses to buy second medium pizza a normal price of 10$ will apply but second pizza will be send for free. Any pizza can be chosen from medium pizza menu.

setup backend

outcome frontend
discount will only be applied once, i.e. if 4xmedium pizza selected , only one of them will get the 30% discount.

Note: that is something i should probably make an option so it would do :
if 2 x medium one of them will get 30% discount , if 4 x medium 2 of them will get 30% discount etc. i will put that on my list of things to do . at the moment , it does not do that

Hi
a couple of things

a) generally , please always start/post your own topic. not only because things will stay somewhat more organised but also because if you were to mark a reply as private , the ORIGINAL POSTER would have access to it which is – let’s say – not ideal and probably not what you would wish….

b) ignoring the above for the moment:
the discounts in that plugin are not accumulative as – in theory – the customer could unintentionally end up with discounts that would exceed the total value of the purchase (although the plugin will never allow negative totals of course)

that said, there is an argument that can be made for adding a checkbox or something to a discount that would allow this to be applied cumulative to others. Alas, this is not yet implemented.

So , as a workaround for you , I wrote some function which – instead of using discounts actually reduces the price to start off with on a given day here

https://www.wp-pizza.com/topic/change-prices-of-menu-items-depending-on-day-of-week/

(this could also be used for all sorts of other things, so i put it in the codesnippets section)

However I do not know exactly what you want to do where on your site, so you would have to tweak it as required. If you need some pointers there, feel free to let me know

Olly