Magic Accuracy
April 4, 2017
15:18
There are two types of magic: Magic with guaranteed hit rate, and magic with a percentile chance (generally status ailments).
Magic accuracy is determined pretty simply: the spell's base success rate, plus the user's level, minus the enemy's level = final chance of success.  Believe it or not, most spells have - at worst - a 66% (2/3) chance of success at base.  Even stuff you wouldn't expect to have it, such as the Black Magic spell Death, is actually an 80% success rate!  Of course, by the time you get it, most enemies will have a noticeably higher level than you...  but this also means that, should you be lucky enough to draw a Blue Mage or Chemist, you can influence your or your enemy's level and raise your success!
Or so it seems.
As you draw towards the later parts of the game, however, enemies begin having Magic Evade (And you can get some of this too).  Magic Evade does NOT effect spells that are guaranteed to hit - for instance, the Fire/Ice/Bolt spells absolutely will hit.  Anything less than that, though - even stuff with a 99% chance to hit - can be stopped via Magic Evade.
Magic Evade does NOT simply reduce the chance of success.  Instead, it is a completely separate chance to block a spell.  Say you have a 70% chance of instant killing an enemy after factoring in level, etc.  But that enemy has 20% magic evade.  Even IF the spell would hit, there is then a 1/5 chance that the spell will still fail, completely separately.  MOST bosses have a negligible amount of Magic Evade, but a handful of bosses near the end of the game, especially the last boss and the superbosses, have extremely significant Magic Evade, and no amount of level manipulation will be able to raise your success rate with spells very high.
In the boss guide, I'll make a point to note the boss' level and magic evade - you can figure out from there if you want to try using certain less-than-completely-accurate techniques on them.