Just one question though... how would you honestly implement this concept? I mean, if BTB is 5* wouldn't a Rabid Thorn Blade be basically 6* level? Just thought I'd ask questions.

Why not model them after their bosses in similar fashion to the originals?

Concerning Polaris/Catalyzer/Static Capacitor for RT's (now RRT)
Sealed Sword & Antigua for JK (now IQ)
and the ever valued FoV for DFV?

Sealed sword and antigua develop an ice branch?
FoV gets a twin?

The Vanaduke mace would seem kind of strange due to the fact maces are usually shorter then swords, but slower, so a mace styled weapon would have to deal a lot more damage then other weapons.

Ice Jelly Sword only makes since because there are no Leviathan/Brandish 3 hit side combo piercing swords. (That I know of.)

Blackhawk was originally a Jelly Jem gun, to have it change to something for Snarbolax seems off.

However, I think there should be some gun for the Snarbolax side of things. Being that there is a Snarbolax Cap, Coat, Barbarous Thorn Blade, Shield,
and a Dark Briar Barrage makes it seem like the only things missing from your character is a gun and trinkets. Snarbolax Trinkets would seem useless being that there are already Royal Jelly Bands and Dread Skelly Charms, the only two Damage types of defense related to Snarbolax. Also, the issue in the Rabid Snarbolax gun is that 1: It would be the only piece related to Rabid Snarbolax, making it green and all the other Snarbolax red. 2: If it causes poison and deals Piercing damage like Barbarous Thorn Blade and Dark Briar Barrage it will be almost identical to Plague Needle.

A fire Polaris would make Polaris obsolete, also we have enough pushing, plowing and blowing weapons. A Quasar gun would make more sense, since there is a Pulsar gun coming from Roarmulus Twins, there should be a Quasar gun. Something like a Graviton bomb, but a gun that pulls things in. (No not a tractor beam.) Sort of like Polaris has large pellets that blow up on contact, Quasar's shots should pull in, like the super-massive black-hole that it is.

The Master Blast Bomb idea seems kind of useless. There are already fire inducing bombs like Ash of Agni (The Indian god of fire), And Master Blast Bomb would never be used again because something with less raw damage, now has fire, which makes it better in the end.

Swarm Fang sounds like a poisonous FoV, but of course there is one already. (Dread Venom Striker.) And Faust is currently the only cursing sword because it was made to be unique. If they were interested in most shadow weapons having Poison or Curse, Shadow would not only be the best damage type, but weapons like Acheron (The river in Tartarous that Charon faried the souls of the dead) would be way over powered with the ability to cause curse.
I think we best keep curse out of things. If this sword were to come out it would be much like Gran Faust, Phantoms use a "Swarm Fang" as you call it, and shoot Faust charge attacks, I don't think they can curse, but this would be an overpowered sword if it could. Thus, Swarm Fang should get a name change and deal Shadow Damage, but not curse. Unless we want another overpowered LD sword for the fun of it. This would help the Striker line though, because most Striker line swords are not the best in comparison to Brandish lines.

All in all, after surviving my sublime critique: +1 to this thread.

Good idea but needs some thought.