Gift cards and free shipping discounts.
Free gifts added to the cart automatically.
A separate "Buy X Get Y" campaign type. You can build these offers as a workaround: How to set up Buy X Get Y offers.
Tiered discounts by cart value in one campaign. As a workaround, create one discount per threshold.
Sale prices that change by stock level or by time of day.
Bulk generation of thousands of unique one-time codes, or importing codes from CSV.
A public API.