I have researched how to build a good Mysterune Deck for a long time, and I have found it must have these properties:
1.It have at least about 1/3 Mysterune Quick-play Spell in the Main Deck, to the Mysterune engine work consistency and countinously, so it just have a few non-Mysterune card.
2.Those non-Mysterune card can Disrupt/Control consistency with just a few card and can Draw or Mill a lot, to support the Control ability of Mysterune engine and make them work at best potential. If you have a few Mysterune Quick-play Spell card, those non-Mysterune must be strong.
You can build a deck with those properties with 40 card quite easily, and there are a lot of Mysterune Decks like this have been top in some Tournament. But how to build a 60 card Mysterune Deck?
To ensure the property 1, you must play all Mysterune Spell card at 3 except the Countinous Spell card, because it is a dead card. But still, you just have 1/3 Mysterune Quick-play Spell in your Main Deck, so the deck must have card/archetypes/engine that can Draw/Mill or Disrupt/Control strongly.
-Among non-Mysterune card, Pot of Desire and Grass is the must have card, and Triple Tactic Talent/Metalfoes Fusion are good Draw card that you should play 1. Another very strong Draw/Mill cards are Maxx "C" (which also Disrupt card) and Reasoning/Monster Gate, but sadly, those card can't be play together because you don't want to have a lot Monster in your deck for Reasoning/Monster Gate, and Maxx "C" whatever how many you play in this Deck is very arkward. So either 3 Maxx "C" or 3 Reasoning+3 Monster Gate, not both. You must choose between strong going second or going first ability.
-Among non-Mysterune archetypes, Tearalaments is the best choice. This archetypes is very strong, it works very well with Grass, it can Mill sometimes and it can Disrupt/Control with just 1 Rainoheart or 1 Tearalaments+some lucky, and the best thing this archetypes can do is El Shaddoll Winda, which one of the best Floodgate in Meta game.
-And is there any good engine for this deck? Luckily, Konami have realeased "the Ancient" archetypes, which can mill 5 CARD with Kelbek/Agido!!! So you can play this deck without Reasoning/Monster Gate by replace them with the engine Kelbek/Agido so you can play 3 Maxx "C" while still have strong going first ability!!! And you can play more Tearalaments monster, like Haufenis, so you have 9 hand trap Maxx "C"/Haufenis/Kelbek for going second!!!
And after add some good card, you now have a good Mysterune Deck as show here. It still weak to hand trap or going second (sadly) but if you lucky, it is very fun to play.