Final Fantasy IV US 1.1 Sneak Mechanics

Final Fantasy IV US 1.1 Sneak Mechanics
Last Updated: 2021-05-31

Prerequisites
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The initial value of the $2F stat is the monster's level plus ten. For
most characters, the default value is 10. The exceptions are: Cecil (paladin):1,
Cid: 20, Edge: 25, FuSoYa: 50. It can be reduced through use of the Cry command.
Each use of the Cry command will reduce each monster's $2F stat by half the
Cry user's own $2F stat. (In practice, this means that Cry will reduce each
monster's stat by 5, as long as characters are vanilla.) If the value reaches
zero or less, it will be reset to one.

(Just for curiosity's sake, this $2F stat is also used to calculate things like
certain timer durations for monsters, and was part of an unused "enemies run
away" mechanic. This list is not necessarily exhaustive.)

Procedure
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1. Select a random value from 0 to 98, inclusive.
2. Add the actor's level to 50, and then subtract the target's $2F stat. If the
   result is negative, set the result to one. If the result is greater than 99,
   set the result to 99.
3. If the previous result is greater than or equal to the random number from
   step one, continue to step 4. Otherwise, go to failure step 1, below.
4. If the target always drops an item, return with no further action.
5. Load the item in the first slot in the monster's drop table. If no item,
   do a basic failure with a "failed" message but no damage. (I don't think this
   is actually possible, at least in SNES Rev 1.)
6. The count of stolen items is generally 1. If sneaking an arrow, however, the
   count is instead 10.
7. If the item being stolen is not already in the inventory with room for the
   stolen count, and there is no empty slot, do the basic failure with a
   "failed" message but no damage.


Failure
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1. Select another random number from 0 to 98. If that value is less than the
   target's $2F stat, the sneak has failed with no repurcussion.
2. Otherwise, the actor will take damage equal to 1/16 of their maximum HP.
   Well, they were supposed to, anyway. There is a bug that causes the low byte
   of the damage value to be clobbered with the slot of the actor. Therefore,
   the actual damage formula ends up being:
           ((<maximum HP> // 16) // 256) * 256 + <actor slot>

Notes
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The two uses of $2F in this routine imply that while Cry will make Sneak more
likely to succeed, in the event that it fails, the use of Cry will make it more
likely to cause damage.

Not every failure method uses the failure steps. Unless explicitly mentioned,
assume failure results in no additional action.

Quirks
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There is a bug with stealing weapons that results in their flags not being set
correctly. While the effect varies per weapon, most weapons, if equipped and used as
items, will cast an unblockable instant death spell. This effect only lasts for
the current battle.