Another Maze of the Blue Medusa conversion for my own reference, but feel free to use it.
Magic Resistance. The Fearful Drone has advantage on saving throws against spells and other magical effects.
Spider Climb. The Fearful Drone can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.
Proboscis. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 16 (4d6 + 2) piercing damage plus 24 (7d6) necrotic damage, and the target’s hit point maximum is reduced by an amount equal to the necrotic damage taken. If this effect reduces a creature’s hit point maximum to 0, the creature dies. This reduction to a creature’s hit point maximum lasts until the creature finishes a long rest or until it is affected by a spell-like greater restoration.