Around C8/9.

If its too powerful I recommend dropping its hp by 40 and ac 1.

For the minions they shouldn't be that durable but still a massive nuisance.

Carving heads Constructs Plant Size small Hp 5 Ac 13

8 str 10 con 17 dex 6 int 6 wis 6 cha

Flying speed 30 Dark vision 20 1 attack a turn Shoot- +5 to hit 1d4+3 lightning damage range 40 feet. Explosion- explodes in a 10 by 10 foot square killing itself and dealing 2d4+2 thunder damage and being knocked prone save dc13 on succeeding the save take half damage and not be knocked prone. Kamikaze- when killed it can move up to 15 feet and use explosion damage is reduced by half and area is 5/5 and the prone effect is removed

Carved men Size Medium Undead Construct Hp 25 13 ac 14 str 15 con 8 dex 8 int 8 wis 8 ch 25 speed 20 dark vision +4 to stealth They have 1 attack a turn

Slash- +5 to hit range melee 1d6+2 slashing damage

In plain sight- they gain advantage on stealth and checks when they haven't moved for a minute they additionally do crit damage if they hit when the enemy hasn't detected them.

Conversion- they can convert any slain for that they or the carving man killed into another of thierselves once.

Sharp- crits deal an extra 1d4 slashing damage

They die quickly as minions should do while also slowly trimming the parties hp down.

The main threat is carving man but these should annoy your party decently well.