Fyndhorn Bow! An awesome card that I didn't know existed until today. Which might be a bad thing, since, if I want to be a great Magic: The Gathering designer, I should probably look at every single card that has ever existed. Well, I wouldn't be expected to memorize everything - 'cause that's insane - and something that Aaron Forsythe, director of Magic R&D pretty much does. Anyway...
I looked to Archers for the abilities that are granted to them due to their bow-wielding, and I've found that Archers/Crossbowpeople do one of three things:
Tap ability to deal damage to an attacking/blocking creature
That last one is a white thing. And green shouldn't really be getting first strike all that often. On a tangential note.
We are redesigning this card that already gives first strike, so it's one of the two latter abilities I want to grant to a creature "equipping" this (Equipment as a type hadn't yet been invented yet at the time this card was released). I saw that Viridian Longbow is the only other bow that exists - and it deals 1 damage to a creature or player. So, I opted for reach.
And voila! I used the same costing as before except had it cost one cheaper since I believe first strike to be a bit more valuable than reach.
Perhaps this is in error, though. For example, there might be an issue with being able to threaten any creature with having reach for the measly price of leaving two lands untapped during an opponent's combat step. Perhaps the best way would have been to cost it at 4, like Spidersilk Net compared to Viridian Claw.
Fun fact: Spidersilk Net is a is a reference to Spidersilk Armor.