The latest in SaGa Frontier formula-cracking. It appears that not -all- of the SaGa formulas make no sense. The Shield Card formula is rather straightforward. It's just nigh-useless. And it's one of the best buff spells in the game. The others degrade too fast to be of any use.
From Zaraktheus:
The Shield spell grants a DEF Buff to the Actor and all its Allies. The size of the Buff depends on the Actor's stats, and is calculated as follows:
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/rd means "Divide and round down".
A:INT = Actor Current INT.
A:WIL = Actor Current WIL.
A:PSY = Actor Current PSY.
A:CHA = Actor Current CHA.
(A:INT + A:WIL + A:PSY + A:CHA)
/rd 24
+ 5
= DEF Buff
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So, the value of the DEF Buff can range from 5--21. The DEF Buff overwrites any previous DEF Buff/Debuff, meaning it doesn't stack in any way, but it also doesn't decay or ever wear off (within the battle in which it was cast).
The DEF Buff will increase your EDV (Effective DEF Value), which is used to reduce damage from almost any damage-dealing attack (unless it completely bypasses DEF, like BoundShot, etc), but so far, all the SCPs (Status Change Processes) I've translated DON'T count the DEF Buff even when they do count your Status FX DEF, so it probably doesn't help at all in resisting Status Ailments. Also, different EPs use EDV differently, so exactly how much benefit you get from a given DEF Buff depends on what attacks you're facing and which EPs they use. A DEF Buff of 5 generally won't mean much, but a Buff closer to 21, especially since it affects all PCs with just one casting, can significantly reduce the party's damage from most attacks.
Unfortunately, the Bosses against whom damage-reduction would probably be most useful often do a great deal of that damage using EP 14 (Boss) attacks, which use EDV in such a way that the DEF Buff will often make much less difference than usual. As a result, Shield may be less help than you'd like just when you need it most.
Also, since the value of the Buff is so heavily dependant upon stats, the spell isn't really as effective until later in a game, by which time you've probably had the opportunity to get much better armor, and so may not need the Buff as much anyway.
Nevertheless, Shield is one of the better Buffs available in the game, and it's not a bad idea to have your highest-stat PC cast it on the first round of any battle you don't expect to win in one or two rounds. It can help to prevent OHKOs and the like, and especially if combined with regeneration effects from VitalityRune, SelfRepair, and/or the monster Syntheses, it can cut down on the need for healing.
