Mechanical Guardian

Mechanical guardian is a very dangerous hostile creature found in underground hidden rooms of all worlds and all biomes.

Behavior
The mechanical guardian remains deactivated until a dwarf approaches it. While in the deactivated form, it is immune to any kind of damage. When activated, it slowly pursues dwarfs, which it can do only in a horizontal line, not being able to jump even a one-block high obstacle.

This lack of mobility makes it sort of easy to be killed by dwarfs equiped with ranged weapons. Although, ranged attacks can take a long time to knock it down because it has a special resistances against magic and arrows.