Everyone is reporting on the fact that the ORIGINAL Mickey and Minnie Mouse are in the public domain. While this is good news, it is important to recognize that that this is not the Mickey and Minnie that we see today. So if you're going to use the public domain versions, make sure you understand what you're using.

The Morning Brew notes these two limitations:

• Only the original versions of Mickey and Minnie, as they appear in Steamboat Willie, are up for grabs. Character details introduced in later years, including their white gloves, Mickey’s classic red pants, Minnie’s polka dots, and their high-pitched voice, are off limits.
• Disney still has a registered trademark on Steamboat Willie Mickey as a company mascot, so folks who use the character’s likeness have to make it clear that their project isn’t an official Disney production.

And if you're looking for a version to use, check out Wikimedia. 

Duke University has a list of what else joined the public Domain this year. Use them and enjoy!