I’ve heard that season 2 is finished. So I removed my old Spinal shadow to be able to create new Cinder shadow.
But those new characters are still nowhere to be found in Shadow Lab.
So my question is when? Will there be another updates before season 3?
You can count on there being new updates before S3 - there’s just too much to add, fix, or do. 
That being said, they just recently added Riptor and Omen into the Shadows mode. They’re staggering the character releases (although we don’t know the exact schedule), so you, like me, will have to wait for Cinder. 
Not next update. They are leaving Cinder and Aria out.