Aerotomaton

Etherflight. The aerotomaton's flight is powered by ether generated from its core. It can hover 5 ft. off the ground, and is immune to effects that would reduce its flying speed unless the core is destroyed. Destroying the core will cause it to fall to the ground and become immobile permanently. 

Magic Resistant. The aerotomaton has advantage on saving throws against any and all magical abilities and spells it is directly affected by. (This does not provide resistance to ancillary effects from spells, such as damage from terrain effects.)

IR Sensors. The aerotomaton is equipped with infrared sensors powered by the core. It knows the location of any creature within 60ft that isn't behind cover.

Core Vulnerability. Creatures can make a targeted attack on the aerotomaton's core, which has 15 hitpoints. When destroyed, the aerotomaton will fall to the ground, and lose both Etherflight and Relentless Pursuit.

Multiattack. The aerotomaton makes two Machinegun Blast attacks.

Machinegun Blast. Ranged weapon attack: +4 to hit, range 40/120 ft., 2 targets (within 10 ft. of each other). Hit: (3d4 + 3) piercing damage.

Precision Pickaxe. Melee weapon attack: +8 to hit, reach 5 ft., 1 target. Hit: (3d6 +4) piercing damage.

Last Resort. When acting as a sentry (i.e. while grounded after having its core destroyed) and a creature moves within 5 ft. of the aerotomaton, that creature gains disadvantage on their next attack roll. Useable once per encounter.