This deck is built around trying to resolve
Spring of the Mysterune as often as possible while not dying. While decking out is technically how you end games, games are decided by how often and how much cards you can draw with Spring of the Mysterune.
One popular variants of Mysterune is Magical Musket. From my playtest, I found them to be rather bricky, and draws with Muskets means no fuel for Spring of Mysterune. Additonally, lack of draws in Magical Musket means finding Mysterune spells to restart Spring of the Mysterune difficult. Live Twins, on the other hands, need far less garnets in deck to function, and the card draws from Ki-Sikil provide valuable chances to kickstart Spring of the Mysterune. In trading off the S/T negate from Magical Musket, Live Twin also provide non-targeting and non destruction removal, which out monsters that would otherwise need to be destroyed in battle, which the deck cannot do.
Spring of the Mysterune
The heart and soul of the deck. search it out with Point of the Mysterune, or Huginn, Wings of Mysterune and make sure it always triggers. Drawing 1 is crazy good, drawing 2 is horrid.
Point of the Mysterune
ROTA of the deck. Use it to fill up the grave with extra spells, or use it after Spring of the Mysterune to round out your hands.
Mysterune of Freezing Curse/ Mysterune of the Brilliant Flame/ Mysterune of Destruction
All Mysterune cards are OPT, so use these turn 1 to summon the fusion, since they are generally dead. But these are the cards you should hold on if possible for disruptions, but feel free to burn them during opponent's end phase to cycle cards and mill their decks.
Mysterune of Slumber
You run 3 because this card is ALWAYS playable, so Spring of Mysterune can trigger.
Mysterune of Disruption / Mysterune of the Golden Droplets / Mysterune of the Raging Storm
Additional names to summon Extra Deck monsters, Golden Droplets -> Disruption mills 7 cards from the deck.
Raging storm can hit pretty high numbers too, but its value mostly derive from being a easy trigger for Spring of Mysterune, and being a finisher to mill the remaining 2-3 cards from the deck.
Live Twin Lil-la/ Live Twin Ki-sikil / Live Twin Ki-sikil Frost
With Secret Password and Sunny's Snitch, there are 6 starters to find Trouble Sunny. Ki-Sikil Frost is not only a ext or ender, but the extra card draw she can provide goes a long way in accelerating your game plan. With Gigantic Splight, negating any Live Twin doesn't stop the play completely, as you can choose whether to get a draw or a pop next turn. Do keep in mind those lines of plays will open you up to Feather Duster or Lightning Storm, with Trouble Sunny, you can activate Trouble Sunny and summon Huginn, Wings of the Mysterune to protect your field spell instead.
Secret Password / Sunny Snitch
Because of the heavy card draws in the deck, and the importance of keeping Spring of Mysterune engine running, running more copies of the Live Twin and their searchers can brick draws from Spring of the Mysterune.
Ki-sikil & Lil-la / Forbidden Droplet
Cards that can out annoying cards that cannot be targeted or destroyed.
Metalfoes Fusion
Good discard target for Huginn, pop it with Lil-La to get a draw. Generally a good card that soften the impacts of disruptions.
Called By the Grave / Ash Blossom / Ghost Belle/ Upstart Goblin / Talents
Free slots in the deck. Talents is a second copy of Called By The Grave.
Deceit of the Mysterune
It is a dead card going first and second. You only search this if you already have a field spell, or want to end the game quicker. In both of those cases, we are already winning, winning harder is whatever. However, drawing this when you are low on cards or going second is terrible.