+5 bonus to initiative.
Can’t be surprised while conscious.
Other creatures don’t gain advantage on attack rolls against the Undead Sheriff as a result of being hidden from it.

The Undead Sheriff can force an attack targeted at it's mount to target it instead.
If the Undead Sheriff's mount is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.

Multiattack. Attack twice with Pistol

Pistol. Ranged Weapon Attack: +5 to hit, range 30/90 ft.,  (1d10 + 3) piercing damage.