In Canada, Microsoft gives a free Lumia 950 if you buy a Lumia 950 XL
That's right, get the big one for CAD 850 and get the small one for free. You probably don't need both, so presumably, you have to find a friend that wants one and split the two between yourselves.
This deal seems exclusive to Canada, the US store just offers a free year of Office 365, same goes for the Euro stores. Although, finding a friend that wants to fly to Canada may be easier than finding a friend that wants a Lumia.
Update, April 26: The deal reached the US. A $650 Lumia 950 XL comes with a free Lumia 950 (which normally costs $550).