The clockwork constructs in Mordenkainen’s Tome of Foes are a collection of machines used by rock gnomes to defend their turf. Combining trickery with extraordinary durability and disproportionate damage-dealing capacity, they share a range of condition and damage immunities along with darkvision and the ability to understand their controllers’ commands—but also a rigidity in their behavior that can only be compensated for by active, real-time control. If they’re sent off to do their work on their own, they do it mechanistically, with no adaptation to what’s going on around them.
First up is the bronze scout, which isn’t particularly strong, but it doesn’t need to be, because it’s basically a self-guided mobile land mine. The key things to note are its burrowing movement, its double proficiency in Stealth, its Earth Armor trait, its Lightning Flare action, and one more trait that’s mentioned in the flavor text but unpardonably omitted from its stat block: “telescoping eyestalks” that let it see aboveground while it burrows below. These eyestalks are crucial, because the bronze scout lacks tremorsense or any other listed way to detect the presence of creatures above it.
This combination of features makes the bronze scout the ideal ambush initiator: Using Stealth to muffle its approach, it scuttles along the ground until it sees movement, then tunnels into the earth and heads toward it. Once it’s approximately in position, it pokes its eyestalks up and looks around, checking to see if its position is correct—that is, if at least three enemies are within 15 feet of it (see “Targets in Area of Effect,” Dungeon Master’s Guide, chapter 8). If it’s not, it retracts its eyestalks and repositions. If it is, it sets off its Lightning Flare, whereupon its waiting allies launch their attack. Since it’s immune to physical damage from nonmagical, non-adamantine weapons, it can take a hell of a beating, Biting back at whatever attacks it. But if it’s seriously damaged (reduced to 7 hp or fewer), it dives back underground, provoking no opportunity attack thanks to Earth Armor, and scuttles away.
The bronze scout doesn’t have to be used in this way, though. It can be used, as its name suggests, simply as a scout, which doesn’t attack at all unless it’s discovered. In this instance, the bronze scout Readies the Lightning Flare action, with the triggering condition “when any creature winds up to make a melee attack against it.” Including the wind-up in the trigger condition is key, because it’s a perceivable circumstance allows the bronze scout to use Lightning Flare as an interrupt, occurring before the opponent follows through with the attack, whereas if the condition were “when any creature makes a melee attack,” the reaction would have to wait until after the attack either hit or missed. (more…)