Your free preview Champion is a Champion you can play for free for today only. It’s randomly selected from the Champions you don’t already own. It changes every day. It may not appear until you’ve played a few Practice matches.
You can play the free preview Champion as much as you want, but note that you won’t earn gold when you complete matches with it unless you have a Premium Membership (see “What is Premium?” for more information about Premium Memberships).
The free preview Champion is unique to you – you might have Cinder today, and somebody else might have Scorch.