#Mermay is a delightful art challenge that takes place in May of each year. You can find more here.
Jake Parker created Inktober in 2009 as a challenge to improve his inking skills and develop positive drawing habits. It has since grown into a worldwide endeavor with thousands of artists taking on the challenge every year.
P.S. It is hard.
28 Days of Melanin
28 Days of Melanin is an art challenge BadLuckVixen13 started in 2017 as a way to increase the visibility of people of color in her own art and hope to inspire others to do the same. It became a sort of precursor for the 1 Million for Black!Hermione Series she’s writing here and on AO3.