Typical Selesnya. Making everyone else play by harsh rules that they themselves gleefully ignore. It's an unusual and non-standard definition of the word "duel" when one side of a dispute presents one champion and the other side gets to respond with their entire army.

The Precon Effect

At this "early" date, if we look at the EDHREC page for [card]Mirri, Weatherlight Duelist[/card], the Signature Cards and Top Cards sections look exactly like the cat tribal Commander 2017 precon where Mirri was printed with the addition of [card]Nacatl War-Pride[/card], [card]Regal Caracal[/card], and [card]Pride Sovereign[/card]. This phenomenon is related to what we have been internally calling "The Precon Effect", where a new commander from a Commander precon has lots of decks in the EDHREC database that are nearly identical to the unmodified precon. This happens even if the cards in the precon are not particularly suited to that commander's abilities. Let's count how many times the word "cat" appears on Mirri's card... One time in the creature subtype. Nothing in the rules text says anything about cats except indirectly, since cats happen to be creatures. While cat tribal can be considered cute, and that cuteness can actually get new players interested in the format, Mirri herself is not really a commander suited to cat tribal. Creature swarms, yes. Cat swarms, not necessarily.

Selesnya Good Stuff

Let's look at the top multicolored cards across all colors and pick out the ones that are green/white.

The most relevant of these cards to Mirri are the ones that have the word "creature" somewhere on them, which applies to most of them. While Selesnya is strongly represented in the top enchantments, it may be a mistake to focus too much on cards that care about our other enchantments. We are in the right colors for an enchantress subtheme, but unless those enchantresses tap to attack in combat, they aren't helping the deck along the same strategic axis that Mirri is using. Also, each non-creature enchantment we add to our deck leaves less room to add another creature.

Commander Voltron

We expect Mirri to be attacking and we would like her to survive combat, so some basic protective equipment is in order. You might prefer auras over equipment. I don't, unless the commander specifically has the word "aura" or "enchantment" on the card. Or unless the aura is [card]Eldrazi Conscription[/card]. I like that one. However, I'm not planning on an enchantress theme. Save that for the [card]Karametra, God of Harvests[/card] decks.

We want Mirri to be tapped during our opponent's turns, so equipment that gives her vigilance would actually be a liability. Since she has first strike, equipment that grants deathtouch becomes more appealing. Of course, haste is good for combat commanders, as is hexproof or shroud, but I generally include a couple specific pairs of footwear in every one of my commander decks.

Token Creatures

More creatures attacking by Mirri's side means more creatures get through combat unblocked. A common method in green/white to have more creatures in the deck than actual creature cards is to have cards that make lots of token creatures. But do they really have to be cats? Let's look for cat creatures that have the word "token" in the rules text.

Hey, we were just talking about some of these. I'd consider about half of these to be playable, and that's really not enough token-making creatures to implement a strategy. If you really want to focus on cats, then your commander should be [card]Arahbo, Roar of the World[/card]. Likewise, if you really want to focus on equipment, then [card]Nazahn, Revered Bladesmith[/card] should be on top. As crew of the Weatherlight, Mirri worked alongside creatures of many different races and backgrounds, so for lore's sake don't focus a Mirri deck just on cats. How about some tiny lifelinking white vampires? Eldrazi scions, saprolings, elves, servos, thopters, insects, hornets, soldiers, angels... I'm just saying you have plenty of other options.

Token Swarm Enhancers

Poke around on the [card]Rhys the Redeemed[/card] page to find your favorite [card]Overrun[/card] effect. Add these to your personal taste. If you can still somehow find joy by casting [card]Craterhoof Behemoth[/card] as your win condition for the umpteenth time, then you are blessed. Add as many enchantments with the words "token" and "twice that many" as you can stomach. You already know what they are... and if you don't, then I just told you exactly how to search for them.

Menace?

If each opponent can't block with more than one creature, then creatures with menace become unblockable.

Unfortunately, there's not much menace here to see within Mirri's colors. [card]Whispersilk Cloak[/card] costs less to equip than [card]Chitinous Cloak[/card]. Mirri generally wants to attack, not tap to crew a vehicle. Odric and the chimera only work if something else has menace, which is looking unlikely since this list is so short.

Out of these creatures, only Kozilek interests me. On that note, remember to add a couple of [card]Wastes[/card] among the basic lands so the green basic land ramp spells can find them.

Rattlesnakes

If each opponent can attack us with only one creature, then it could make sense to add a handful of dedicated blockers with upside. Perhaps some Ixilan dinosaurs with the enrage ability can now find a home in a Mirri EDH deck. The following list can be found by searching for cards in green/white that have both "whenever" and "is dealt damage" in the rules text. The particularly juicy ones can make a pile of token creatures when they get hit.

Tap Stax

Of course each of your opponents can attack you with only one creature, and they probably will. <TAP> But it won't be that creature. The one you just forced to tap. That one. A possible way to approach this deck is to consider a non-blue subset of cards from [card]Derevi, Empyrial Tactician[/card] decks. Pour on enough of this style of play, and you might as well go full-on [card]Gaddock Teeg[/card] and force everyone to try to play Tiny Leaders with their non-Tiny decks. Then everyone will love you.

EDH veterans are likely familiar with many of the following cards found by searching in green/white for "opponents control", "enter", and "tapped".

Another Derevi-style way to enhance Mirri's offensive ability is to use cards that can tap opponent blockers, so they can only block with their second-best creature (or third-best, etcetera). Here's a green/white search for "Whenever", "tap target creature", and "opponent".

The Deck

Maybe the mana curve on this is a bit high. Maybe some of the Good Stuff could be swapped out for more token makers. Maybe it doesn't need a slight Eldrazi subtheme. So many questions. Have a deck!