I had some thoughts about the different spheres and how they typically begin games this morning. Thought I'd post that here for the public's edification.
First, let me say that a file's opening book (to borrow the term from chess), which we will here define as the first three Set Phases of the game, is perhaps the most important factor influencing a file's win rate, other than file construction itself. However, the opening book is the place where file construction and file piloting are perhaps most closely connected.
(For example, when I construct my files, I start by determining what my opening book will be, and I use the upper-left slots of my file for that book. It's an aesthetic move, but it also helps me pick a file back up after switching back and forth, because I can see at a glance what my opening book will be.)
Why are these first three set phases so important? In short, they have the greatest ripple effect on the rest of the game. It's possible to create a wide SP gap between you and your opponent in the first three phases, setting up your file for victory before you start the routine process of deploying units and attacking.
(For example, if your opening book is Shade - Proxy of Soul Animus - Crest Saboteur Knight, you've generated 5 effective SP through raising sphere levels, and you've possibly drained 1 SP from your opponent. In other words, if your opponent's opening book was SP-neutral, you're effectively 6 SP up before the real fight even starts.)
So, what is an effective opening book? Most spheres have several opening books that are generally accepted to be "optimal" or "the best" in that sphere. To coin another term, an "optimal open" is a Turn-1 play that allows you to play a Level 3 spell on Turn 2, regardless of your opponent's play (also known as "dodging Shade"). Refess and Falkow in particular have the most common "optimal" opens. For example:
Refess—Put 4 SP into sphere levels and play Emerald Carbuncle.
Falkow—Put 3 SP into sphere levels and play Mechanical Bat.
Of course, the best "optimal" Turn-1 play for almost any Lawtia deck is Shade.
Gowen is an odd case in that it doesn't have a commonly-accepted optimal open. Most Gowen decks go to Gowen 3 and play a Level 2 unit as their Turn 1 play. This allows a Turn-3 Level 3 unit, instead of a Turn-2 Level 3. However, for many rush decks, an "optimal" open is unnecessary, because the deck features a mix of units between Levels 1 and 3 and can adjust their opening book in a fluid manner to counter the enemy's opening book.
For example, a generic Gowen rush file could use any of the following opening books:
Alraune -> Dryad -> Level 3 unit
Alraune -> Man-Eating Tiger -> Salamander
Man-Eating Tiger -> Kurina -> Salamander
Kurina -> Salamander -> Level 3 unit
Obviously, this doesn't even begin to cover the many options.
Another corner case that is still quite relevant to ranked play is Falkow's Witch Queen Catherina open. This famous open is considered sub-optimal, because it loses 1 SP to the notorious Shade open, but it is nevertheless a powerful start to any Falkow deck's opening book. The player levels Falkow to 2 and sets Catherina, then receives 1 SP from Catherina's open skill in the form of a 3rd Falkow level. From this first turn, the player has several options:
Owl Sage -> Level 3 unit (usually Mage Knight Vanguard)
Level 3 unit -> Owl Sage
Meaning of Failure -> Level 4 unit (or the Level 4 summoner unit)
Proxy of Sea Oseon -> Wandering Bard (for multisphere files)
And of course, many other options.
The reason opening books involving Shade, Catherina, Emerald Carbuncle, or free-reviving Level 2 units are so commonly used is because they are tried-and-true ways to generate SP advantage in the early game. We can see by analyzing these first-turn plays that the only truly optimal first-turn play is Shade, because it is the only play that will at least maintain SP parity in any scenario, EVEN BACKLASHES, and is the only play that allows a turn-2 Level 3 spell in every scenario, EVEN BACKLASHES. The lesser opens of Emerald Carbuncle and Catherina are nearly as good, but Carbuncle falls short in the backlash scenario, and Catherina falls short in the Catherina/Shade matchup and the backlash scenario.
I'll stop here, but this is nowhere near a complete analysis of opening books. I just wanted to analyze WHY common opens are common, and get people thinking about how to improve the opening books of their own files. As a final note, I want to emphasize that while linear opening books (such as Shade -> Animus -> CSK) are powerful in a vacuum, the best opening book is both powerful and fluid; that is, it generates a large amount of SP advantage while being open to change according to the opponent's plays.
With that, I open the topic to discussion. Thank you for reading!