What is a proper CR for this homebrewed bloodborne-esque NPC?

Question

Having ventured into the lands of gothic horror for a soon upcoming adventure, I wanted to create something a little more out there from the normal rules of D&D 5e. So I came up with this idea that the party would meet a Hunter of sorts; one who hunts monsters with brutality and efficiency (and who ends up going insane). So I created this template and I hope to get the answer to the question...

What would be the proper CR for a monster with these abilities?

Because of the specific ability this creature has, I have some doubts about the normal method of CR calculation which is why I am bringing it to you all.

I use a CR calculator; plugging in the information, I got a CR of 5. This creature has a Defensive CR of 4 and an Offensive CR of 6. Of other note, it lists CR based off HP as 2 and AC for Health CR as 13. The Max CR for its AC is 12. Additionally CR based off Damage, Attack Modifier for Damage, and Save DC all are 6 while the Attack Modifier Min/Max CR is 8/10. If any of that helps.

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Vastoyan Hunter

Medium humanoid (human), any alignment

Armor Class: 17 (breastplate)
Hit Points: 90 (12d8 + 36)
Speed: 30 ft.

STR - 16 (+3)
DEX - 16 (+3)
CON - 16 (+3)
INT - 11 (+0)
WIS - 15 (+2)
CHA - 14 (+2)

Saving Throws: Dex +7, Wis +6
Skills: Deception +6, Insight +6, Intimidation+6, Perception +6, Stealth +7
Damage Resistances: poison
Condition Immunities: -
Senses: Passive Perception 17
Languages: Common, Dwarf
Challenge: ???

Traits

Close-Quarters Expert. Being within 5 feet of a hostile creature doesn't impose disadvantage on the vastoyan hunter's ranged attack rolls.

Quick Silvered Weapons. The vastoyan hunter's pistol attack and hunter's blade attack are considered magical for purposes of ignoring resistance.

Actions

Multiattack. The vastoyan hunter makes 3 melee attacks.

Hunter's Blade. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (2d4+3) slashing damage.

Shoving Kick. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: If this attack succeeds, the target must succeed on a DC 16 Strength saving throw or be either pushed 5 feet away or knocked prone (the hunter chooses which).

Pistol. Ranged Weapon Attack: +7 to hit, range 30/90 ft., one target. Hit: 9 (1d10+3) piercing damage.

Reactions

Parry and Riposte. The vastoyan hunter makes a pistol attack against a creature that is attacking them with a melee attack. If this pistol attack succeeds, the creature's attack ends and the vastoyan hunter may make an immediate melee attack against the attacker with advantage. If this melee attack succeeds, it is a critical hit.

Answer 1

Apparently it seems to be the special reaction you gave your creature that is making you worry about balance. Let's see how powerful it really is:

The vastoyan hunter makes a pistol attack against a target that is attacking them with a melee attack. If this pistol attack succeeds, the target's attack ends

Due to the hunter having Close-Quarters Expert and +7 to hit, it'll generally roll a 17 to hit. Assuming its target has about the same AC as it, 17, it'll hit with this pistol attack about 50% of the time. So per round, it'll deal 50% of its pistol damage (9/2=4.5), and prevent 50% of your PC's melee attack. We're not sure what that damage would be, so let's assume it's about the same power level as the hunter's once again, so it'll prevent ~5 per attack, so with multiattack that's at least 10 damage per round.

and the vastoyan hunter may make an immediate melee attack against the attacker with advantage. If this melee attack succeeds, it is a critical hit.

So then, if it connects with its pistol, it has a +7 attack with advantage against its target. That should hit about 75% of the time (if AC 17), so 37.5% chance to hit each round, because the pistol has to hit first: 8*0.375=2 (more or less). But the attack deals double damage (more or less) because it's a crit, so it'll deal an additional 4 damage per round.

(Note: Shoving Kick doesn't have damage specified, but I imagine it'd be less than the blade attack to compensate for the shove so we'll just use the blade attack here.)

So in total, that reaction will give the hunter an additional 9 damage per round on average, and prevent at least 10 damage to them per round. If the hunter is intelligent enough and uses it on a Rogue that would get sneak attack, more damage will be prevented.

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So, how does this compare to other creatures in the MM?

The Chimera (MM, p. 39) is CR 6. Its AC is lower (14), but it has more health (114 HP). It has no ranged attacks (well, apart from the breath but I'll come back to that later), but it does have a flying speed of 60 feet. It makes 3 attacks per round at +7, just like the hunter. I think it can be compared to the hunter on this basis.

Once every three rounds (on average), it can deal additional AoE damage on one of its three attacks this round using its fire breath (this does replace one of its usual attacks). If its breath only affected one target, it would deal at least an additional 4 damage to that target that turn. If it can hit three targets with its breath, that would be at least 4+15+15=34 damage that turn, if the characters all succeed their DEX save. So once every three turns, that make an additional 11 damage per round. If any characters fail their DEX saves, that's just free real estate.

In the end, that's quite similar numbers to the hunter's reaction, which means that CR 6 should fit nicely. The hunter is intelligent, so as I commented, depending on the party, the damage prevention could be a lot more powerful than against a different party. But this factor could be an interest mechanic for your players to play around: wait until the hunter used their reaction on an attack of opportunity, or used the Parry and Riposte on the tank, before letting a high damage melee PC attack.