If you're looking to maximise profit and increase AOV for orders, or need a special offer to run during the mid-sale, then this is a great offer to try in your cart.
Method 1: Add another Product A and get X% off
Your customer has an item in the cart (Product A) and you want to upsell another one with a discount e.g. 20% off.
To do this, use the 'Bulk Discounts' Cart Block to enable an offer for the SAME product.
Method 2: When Product A is in Cart, Show Product B Upsell and get X% off
Your customer has added an item to cart (Product A) and you want to upsell another item (Product B) and give them a discount of X% off.
What you need to do is setup a discount in your Shopify Discounts (not in the Unicorn app) and make a Buy X Get Y for the cross-sell you want to offer.
E.g. Buy Product A and get 20% of product B.
You can then offer the Cross-sell (product B) in the cart and change the title to 'add me and get 20% off' and then the customer can benefit from this offer.