The Royal Champion in Clash Mini
With the Royal Champion you deal damage and stun minis to gain value to overtake the board and you always want to pair her with minis that can hold the frontline so you can deal damage and stuns from the back until you gradually add other minis to the board – primarily she goes well with another mini like the Electro Wizard that can stun as well to keep your opponent#s units in a stun lock.
Best Position
Always place her off the center tile and never directly in line with a frontline mini to prevent enemy units from gaining value from that (e.g. the Magic Archer). I have an image below to show you waht I mean:

The Best Decks with the Royal Champion in Clash Mini
Let’s now take a look at the decks. Please mind, this list gets updated each time I update my meta tier list of the best decks in Clash Mini and it also goes hand-in-hand with my usually monthly updated tier list of minis/heroes in Clash Mini here. I highly recommend you to also check them out!
Paired with a number of well-performing frontline minis, you keep your opponents mins busy while the Roal Champion act from the backline, along with the Elextro Wizard dealing stuns that are vital for disruption.

Conclusion
I hope this helps you if you want to find a deck with the Royal Champion as hero in Clash Mini that performs well in the current meta of Clash Mini. If you have more questions or you might have a deck that I should test and maybe add here, please post a comment below and I will be happy to reply.