Why was Frilled Mystic created rather than reprinting Mystic Snake?

Because it was part of a MMNN cycle (two mana of the first color and two mana of the second floor).

Got any birthday trivia for Mystic Snake?

I didn’t know it was Mystic Snake’s birthday. : ) The card looks a bit odd now as a multicolor card but at the time Green was more of a flash color than Blue. Also the 2/2 instead of a 1/1 was supposed to be Green giving it a little extra heft. The more interesting thing that many might miss is that we like to occasionally do overlaps in multicolor and thus card captures one of the overlaps - snakes! Snakes are mostly seen in Blue and Green (okay and sometimes in Black). Happy Birthday Mystic Snake!

I think the game is better off if we don't see Mystic Snake in Mono-U, feels like the type of thing that could be obnoxious in the modern world with Resto Angel and other blink effects being so prevalent.

I was pointing out that the modern color pie could do it not that we should do it.

I understand the flavor of blue and green being enemies (not really) but it is very hard to see it that way while playing magic. Considering just how strong U/G really is in most cases. Then consider Mystic Snake exists....how can we really continue to think blue and green are "enemies", when they should be called "allies separated by red, black and white."

The green/blue conflict is nature vs. nurture. Green believes you are born into the role you will serve with innate skills that come from genetics. Blue believes you are a blank slate and that you can learn and use technology to improve and become anything.