Having an item that grows more powerful as someone uses it is a time-honored tradition amongst games of all kinds.
Having an artifact of lycanthropy be cursed is a similarly venerated concept, but consider having the item inflict a feral version of the lycanthropy curse on its victims to be a more cohesive idea, rather than simply transforming them into a beast.
When it comes to tiered items that grow in power, you don't want to have the criteria for improvement in the item's description. Items are meant to be base points from which you can jump off, using the item as a foundation for creativity. By having the criteria for power gains in the item description, you lock those options down. These should be personal journey goals, or lore hidden away somewhere in the world. In short, quests, not properties.
I like the idea of marking weak enemies, but consider something simpler like "When you reduce a living creature to below half of their maximum hit points, you can use a bonus action to cast hunter's mark on them without expending a spell slot, having the spell prepared, or needing to maintain concentration. When a target marked by this property dies, you regain Y hit points and the spell ends." This way, you have established rules to govern this effect and you don't screw the player out of hit points if they don't get the killing blow.
For phase 2, you need to be specific about the DC that a target needs to beat. You should also be very careful about creating a situation where a player (who likely has multiple attacks) can force saving throws every time they attack, as that will significantly bog the game down. Personally, I think bonus damage and movement reduction is plenty, there's no need for even more damage and an extra save.
For phase 3, again, advantage on all checks for a given skill is sort of like saying "Here I don't really care to make things challenging for you, so you can basically just have the information you want - except instead of just saying that you know it, I'm going to make you roll anyhow to hide the fact that I don't want you to be challenged." In short, a bad idea.
Phase 3 also adds an incredibly powerful, unlimited AoE fear effect akin to the crowd control effect of incredibly high CR enemies. Limited to 3-5 times per day (since the character who gets this is almost certain to have a strong Strength score) is not a meaningful limitation. Speaking of limitations, you should ensure that a feature that you want a player to have always has a minimum possible value. In this situation, if someone got this item and for whatever reason had 11 strength or less, they wouldn't get this feature at all. I would recommend making it once per day, period.
The miniature paladin aura is a really powerful feature, itself being worthy of a very rare or possibly even legendary quality item.
Balance assessment: This item is wildly powerful and should never, ever be given to a player. If it wasn't enough that you gain a ton of extra damage from this weapon (weapon + 2-3d6 + 3) and often as much as +5 to attack, blanket bonuses to saving throws and an incredibly powerful crowd control effect would've been plenty. And that's not considering the other effects.
You want to avoid specifying exact critical ranges on items, because class features can change them. For instance, a 15th level Champion Fighter can crit on 18, 19, or 20 with any weapon except this one, which limits his critical threat range to 19-20. Use wording that just improves (+1 bonus to attack rolls) rather than changes (you have a +6 to hit with attacks using this weapon) or hedges (you deal X damage, unless you deal more).
Shifting forms is a neat idea, but it can create a lot of overhead for the person using it. Also keep in mind that bonus dice damage is a lot stronger than it seems like it is; 1d4 is at minimum equivalent to a +1 bonus to weapon damage, and as much as +4, and that's on top of the weapon's natural +2 bonus.
If you're going to have an item assume a character can cast a spell, it is a good idea to have the item require attunement by someone who can cast the spell. "(requires attunement by a ranger) etc."
Multi-round effects can be annoying to track, but the real issue with Sunburst Shot is the total lack of saving throws. Anyone unfortunate enough to be in the area of this effect takes damage and is blinded, no chance to avoid, and you are guaranteed to apply it to at least one creature of your choice within that range. Give it a saving throw to take half damage and avoid the condition, at least.
Starfall shot reads like you make 6 actual attacks, meaning 6-12 attack rolls. That's a huge amount of overhead; instead, use a saving throw in a shaped area (cone, sphere, cylinder, etc.). Or, have them all based on the same attack roll. If you use an attack roll from a weapon, you should be specific about whether the damage replaces or happens in addition to the normal attack damage.
"Regalia" usually refers to more than one item, often a type of clothing.
Use item standards. By renaming charges into something else, you increase confusion and uncertainty for no gain.
By renaming charges, this reads less like a magical item and more like a new feature for a class. Avoid this; you are making items, not classes.
Again, you need to be specific about a DC (or at least how a DC is calculated) any time you use one. Though I did try to intuit what you were going for whenever this came up, you should be specific about how to activate a given item.
It's clear that you're using a homebrewed gunslinger class or archetype for this. At a guess, I'd assume it was Mercer's Gunslinger. I can't speak to the balance of how this affects that since homebrew (even when it's as good as Mercer's stuff) isn't part of the natural game. You really should have said that you were using other homebrew material before asking us to assess anything, it does matter.
Once more, specify whether damage effects replace or happen in addition to normal (results 8 and 12).
This table has 3 negative effects which, when considering the probability on a 2d6 roll, have a combined chance of happening around 28% of the time. That's a really high failure rate, but you're going for a gambling theme, so it makes sense. I would actually consider trying to increase it and have some of the negative results also have positive effects; you deal 2d6 damage to yourself, but gain a grit point. The weapon misfires, but the target takes twice as much damage, etc. These are more interesting and make failures feel less punishing, while still being relevant factors.
I would do away with charges entirely on this item and go for a limited number of uses per day. It's already at 5 uses per day with a chance to recover 1-5 uses each day, why not just make it 3 times per day and give them that consistency? Of course, if you're going really hard on this gambler theme, consider increasing the cost of using the roulette and having the dice be really big. 20 charges, 4-5 charges per use, you regain 1d20 charges per day. Some days you'll regain a lot of uses, some days you'll regain few. Personally, I think the roulette table should have all of the randomness on the item; it's easier to use something that may backfire on you if you don't also have to worry about not being able to use it for a few days.
These items are all over the place. Some are way too powerful to ever be in a player's hands, others are barely items of note.
There are a few lessons I think that you might take away from this:
An item should never be better at being a class than a player of that class.
An item should never make a player better at being a class than a player of that class.
An item should never be so complex as to supercede the player.
An item should have a cohesive thing. Avoid making items that look like cherry-picked effects that "sound nice to have" but actually have no thought given to whether they're fun to use or not.
When you're making any kind of homebrew content, be specific. Do not assume the reader knows what you meant, because while there may be some that do, there will be many more that do not. You want your content to be usable in a lot of situations, not just one very specific one.