I gotta say, I like these. I'll try to give an individual judgment for each of them:
Nucleus Neutralizer - I'll be honest, cool as it is - that's some
high damage it's got there. Since it's the endgame Sniper Rifle, that's to be expected, and of course there's the slow fire rate to offset it, but add some damage boosting buffs and a nice reforge and it can get nuts pretty quickly - especially with that debuff backing it up if it's going to score crits frequently. But I'm just going off numbers here. I don't actually know how this thing would compare against the existing Celestial stuff. Oh, and I like the idea of the blue flare aesthetic.
MIRV Launcher - No real criticism here; I think it's fairly balanced and seems like fun to use with the splitting rockets. I'd probably use it over Celebration just for the fun of causing explosions everywhere.
Fist of Helios - HELL YEAH! I LOVE IT. I've always wanted to have a genuine punching attack in Terraria. The closest we have right now is using Arkhalis and pretending you're punching at high speeds. But that brings me to my main point for this: Rather than being a sword-type weapon, I say it should be something very similar to
that, with rebalances if need be. This is mostly because I'm sure I can speak for a lot of people when I say it would be awesome to punch the crap out of a mob in anime-style; think Dragon Ball, Hokuto no Ken, JoJo's Bizarre Adventure. An animation akin to that lends itself to this weapon's mechanics, I think.
Melter Trident - This is also cool! I like the sprite, and that ethereal replica mechanic is interesting. It doesn't really scream 'overpowered' to me either, although I think it might render the Solar Eruption obsolete between itself and Daybreak.
Stellar Mirror - By itself, it's already a cool weapon; I'm a sucker for beams and constant energy streams when it comes to spells in this game. As much as I love the team attack, though, I don't know if it's possible to program that in.
Dubstep Cannon - Literally perfect.
Stardust Construct - I'm loving this as well. I honestly don't like the Rainbow Crystal or the Lunar Portal, but this seems much more useful to me.
And if this makes a difference: These weapons are what convinced me to make an account here. Just so I could give my support.
Great job!