5e Dmg 274

I will soon be running a 1 shot for a new group of players and just want a bit of critique on the boss monster.
I have not played in a wee bit over a year and not DM in 5E before, we are using this 1 shot to see how well we gel as a group before jumping into a full campaign so I would like for this to run well.
The party will be 6 - 8 level 3 characters, they will have spent some resources so will not be 100% fresh, but will likely complete a short rest just prior to the fight
I am using a modified Hook Horror, smaller than a normal Hook Horror with a faint red glow. Its hooks burst into flame during combat and its arms are a bit long/gangly to maintain its 10ft reach with its hooks
Burning Hook Horror - Medium Monstrosity
Str 18, Dex 12, Con 15, Int 9, Wis 12, Cha 7
AC16
Hit Points 86
Speed - 30ft, Climb 30ft
Saves - Con +4
Skills - Stealth +3, Perception +3
Senses - Blindsight 60ft, Dark vision 60ft.
Damage Resistance - Fire
Abilities
Echolocation - The Burning Hook Horror can't use its blindsight while deafened
Keen Hearing - The Burning Hook Horro has advantage on perception checks that rely on hearing
Actions
Multi Attack - the Burning Hook Horror makes two Hook attacks
Hook - Melee weapon attack, +6 to hit, reach 10ft, 2d4+4 piercing damage plus 2d4 fire damage
Fire Breath (recharge 5-6) The Burning Hook Horror exhales fire in a 15 foot cone, each creature in that area must make a DC12 dexterity saving throw taking 6d6 fire damage on a failed save or half as much on a success.
Legendary Actions
Attack - The Burning Hook Horror makes a single Hook attack
Fire Belch - The Burning Hook Horror belches out a small glob of fire targeting one creature within 20ft, +3 to hit, 2d6 fire damage
Smoke & Cinder (costs 2 actions) - The Burning Hook Horror exudes burning smoke filled with hot cinders through vents in its back. The smoke fills a 10ft radius around the Burning Hook Horror, all creatures within the area of effect suffers 4d6 fire damage, Constitution save DC12 for half, as they inhale the burning smoke.
Is this too strong or too weak for the proposed 6-8 level 3 characters?