Honestly shining bow would work best on units that can ploy. Since you can just run res ploy and lower your opponent's res, which makes the +7 damage effect activate more often
Or res smoke could work too on units that cant run ploys like your suggestions
But sadly L!Robin is the only unit can you can get it from
Res ploy isn't needed against the majority of the cast. The units that don't have 5 more def than res are mages, dragons, certain other tanks (ex: Hawkeye, Sheena), and squishy units like Karla and Soleil. Against most mages the +7 damage isn't necessary (and res ploy wouldn't activate it anyways), and against squishy units (including mages) brave bow tends to be better anyways. That leaves the mixed bulk units. Res ploy is definitely an idea, but if you're using desperation it's probably preferable just to give up your defenses altogether, and if you don't then you need def vs non-dragons (and walling adaptive damage just takes too many stat points for ranged units with lower BST to pull off in most cases).
I tend to say that if you really want to combine the bow with res ploy, get your teammate to ploy for you.
To piggyback off this, if you're going to use a ploy, choose Defense Ploy! Defense Ploy will add five extra damage regardless, allowing for the majority of the cast to take +12 (and who isn't running an attack buff these days; let's make it +18!)
Assuming you were running a neutral Nina, that's an effective 62 attack with 37 speed. Moonbow Heavy Blade Seal looks mighty fine on her this way, allowing for Player Phase KO potential against most enemies, without having to be threatened to be in the range of mages.
Shining Bow is a lovely little toy in my opinion, and I can't wait for a busted archer to come along to really show off it's power. Someone like Halloween Jacob, but that isn't armored, because with things like Bold/Vengeful Fighter, there are just better options.
I guess the argument against def ploy would be that if it drops the enemy's defense too low you could lose Shining Bow's effect, but it would only be a net loss of two damage since def ploy would grant you +5, and I'd guess that overall it would help more than hurt, since there are plenty of units with very high def and almost no res to speak of.
Faye and *maybe* LA!Roy are currently the non-Jakob archers with the best mixed defenses and enough res to ploy (borderline in Roy's case), if you're looking for non-armored versions. They're both slow as mud so would likely be relegated to enemy phase builds, but I keep thinking how Faye and her 30 atk in particular would love the extra damage from Shining Bow.
If you're afraid of the instant black luna or something like that, yes. I think instant specials are rare enough to justify trying to sustain a little with renewal. It's kind of like having 5 more def. Without guard it's a ORKO or die setup, but I'm ok with that on 53 atk + 7 and a moonbow or bonfire.
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