50% discount on every second product

Hi,

There are ways to do that.
You could do it with several prices in the product (1 per quantity) or several auto loaded coupons (1 per quantity per product).
So it might be tedious / impractical to set that up if you have a lot of products or if your customers can purchase a lot of quantity on the products.
Also, I would recommend to check on AWOCoupon:
awodev.com/products/joomla/awocoupon
Their solution might allow you to setup coupons to do that more easily, but I'm not familiar with their solution so I would recommend to directly check with them.