Mirri fills a niche role, directing combat so concretely, and her Dueling Grounds as a legendary creature design could be the inspiration for more artifact/enchantment turned legends designs in the future
To help you along your path here are a few general tips right now
As I mentioned before, the most powerful way to build Commander decks with MDFCs is to cut five or six lands (usually basic lands or other utility lands that tap for one color of mana) along with two or three spells and replace them with MDFCs so that you end up with something like 31 or 32 "real" lands but 40 or 41 total lands
This white creature basically does the same as long-time EDH staple Reclamation Sage, but with vigilance and with a card-draw activated ability on top to make it a true powerhouse
Body Count | Illustration by Vladimir Krisetskiy The maximum number of copies you can have of a unique card in a Constructed deck is four
It is easy to open the Decks menu, add several cards you like, and end up with a list that looks fun but struggles to set up consistently