In a meeting, will give the full answer with RR page numbers later, The short
1) Yes. It's just applying a modifier -1 to that icon type (You can also choose a 0 STR character for Plaza of punishment or dracarys
2) Yes, 0 base, -1 nymeria + 1 edric +1 edric = 1.
This shouldn't come as a major surprise - we've been working with this for a while with the ability "Confinement" (which, as has been asked before, can be used on, say, Edric) - and just applies a -1 modifier to each icon type.
Here comes the long form answer. Nymeria's text requires that you choose a character, and then it applies the following modifier; -1 icon of your choice to that character / +1 of that icon to Sand snakes.
- The first thing to note is that the only targeting restriction (choose indicates a target) is a character - the icon is chosen, but not targeted.
- The second is that all icon modifications work like this; I've often had people ask whether Nymeria can remove Arya's icon or whether Arya's ability "sets" Arya to already have an icon. I use the same analogy there I'll use here - pretend these are STR modifiers. If Arya said "while she has a duplicate, she gains +1 STR" you wouldn't argue that after applying Dracarys, she stays at 3 STR! Nymeria basically works like a -1 STR/+1 STR modifier.
- The third thing people tend to ask is whether the icon can be gained if it wasn't actually "lost" from the first character - here the answer is easy. The icon removal and icon gain are tied by an AND, not a THEN - they're not conditional at all. Even if they were, the latter portion would be conditional on "the succesful application of a -1 modifier", not dependent on going from 1 (or more) instances of a mil icon to 0 (or fewer).
- Lastly, some players object because they think the icon loss (or gain) might be subject to the rules prohibiting initiating an action that wouldn't change the game state (xxAn ability cannot initiate (and therefore its costs cannot be paid) if the resolution of its effect will not change the game state.) if used on a character without the icon. Again, the paralell here is STR modification - an effect that reads "until the end of the phase, that character gains -2 STR" *could* be used on a 0 STR character (or a 1 STR character participating in a challenge against Danaerys) - because it will succesfully apply a modifier that forces us to recalculate the total (even if the total doesn't change).
A lot of players have trouble with this, but it's all derived from the same entry in the RR: "Modifiers" p13 (which I've pasted below). Traits, cost, keywords, icons, initiative, reserve, gold and STR are all treated the same.
So in the end, when Nymeria strips a mil icon from your unsworn apprentice (0-1=-1=0), then you initiate Unsword Apprentice's ability to give it a mil icon (0-1+1=0), then Syrio's ability grants him another (0-1+1+1=1), you're just adding modifiers. The difference between this and STR is that the game (to date) only cares whether you have 1 or 0 icons/traits/keywords of a relevant type, while STR (and gold, initiative, reserve), every increment above 0 counts.
Some abilities may ask players to modify values.
The game state constantly checks and (if necessary)
updates the count of any variable quantity that is being
Any time a new modifier is applied (or removed),
the entire quantity is recalculated from the start,
considering the unmodified base value and all active
xxThe calculation of a value should treat all modifiers
as being applied simultaneously. However, while
performing the calculation, all additive and
subtractive modifiers should be calculated before
doubling and/or halving modifiers are calculated.
xxFractional values are rounded up after all modifiers
have been applied.
xxWhen a value is “set” to a specific number, the set
modifier overrides all non-set modifiers (including
any new non-set modifiers that are added during the
duration of the set value). If multiple set modifiers
are in conflict, the most recently applied set modifier
xxA quantity cannot be reduced so that it functions
with a value below zero: a card cannot have
“negative” icons, STR, traits, cost, or keywords.
Negative modifiers in excess of a value’s current
quantity can be applied, but, after all active
modifiers have been applied, any resultant value
below zero is treated as zero.
Related: Base Value