With the global pandemic, Santa is forced into lockdown. But he still needs to deliver gifts to the children of the world, and so he hires a replacement.
The Mandalorian needs money to pay Grogu's food bills, and so he takes the job together with his helper.
This ornament depicts Mando and the Child riding in Santa's sleigh, loaded with gifts. (The mesh for the Child and several details on Mando's armour are taken from pre-existing models online, but the repository that I used did not list the original author's name. Please feel free to give appropriate credit in the comments section.)