Kruthiks are a refreshing change of pace: a straight-up monster that just wants to eat, have babies and otherwise be left alone. They come in various sizes, but all of them have in common a high armor class, burrowing and climbing movement, darkvision, tremorsense, and the features Keen Smell, Pack Tactics and Tunneler.
Ordinary young and adult kruthiks have a balanced ability contour favoring Dexterity. This would normally indicate a bias toward ranged combat, but young kruthiks lack a ranged attack, and in adult kruthiks, the bias is slight, almost insignificant. Thus, they don’t fit neatly into any one single combat profile. On the other hand, their Intelligence isn’t high enough to indicate tactical flexibility. I’m going to interpret this to mean that they may start combat in any number of ways—brute melee fighting, ranged sniping, scrappy skirmishing, hard-and-fast shock attacks—but whichever of these they choose, they generally don’t deviate from.
Because their ability contours offer so few clues about their fighting styles, the importance of their burrowing and climbing movement and their Pack Tactics and Tunneler features is magnified. Young kruthiks are disinclined to fight enemies they don’t outnumber—at least 3 to 1. Adult kruthiks don’t necessarily have to outnumber their enemies, but they’ll never fight in a group of fewer than three, and four or five is a more typical squad size. Since young kruthiks have only melee attacks, they have to swarm their enemies; adult kruthiks can combine melee Stab attacks with ranged Spike attacks (akin to a porcupine throwing its quills) and gain the benefit of Pack Tactics as long as least one of them is engaged in melee with a foe.
Kruthiks’ burrowing speed isn’t fast enough to use to flee, although the tunnels created by young kruthiks aren’t wide enough for Medium-size characters to pursue them through. A more interesting application of their burrowing and tunneling ability is to expand their tactical possibilities in the extremely limited milieu of tunnel fighting.
Kruthiks live in networks of tunnels no wider than they are, so how are they going to use Pack Tactics to gang up on intruders? Like this: An adult kruthik can bait enemies into following it, single file, into a tunnel. Other adult kruthiks can dig boltholes on either side of the tunnel, just deep enough for themselves, and Hide in them. Thanks to their climbing movement, they can even dig one overhead. When the lead pursuer reaches their position, the retreating kruthik suddenly stops and turns on its pursuer, and it and its companions all attack at once. Another kruthik can then come up behind the previously retreating kruthik and supplement its allies’ melee attacks with ranged Spike attacks; its target will have half meat cover, but the advantage the spike-throwing kruthik gains from Pack Tactics more than makes up for this. (A second kruthik would have a harder time, having to throw its spikes past two allies in the tunnel, which I’d say would provide three-fourths cover to the target. Attacking advantage isn’t enough to make up for this penalty.)
A more open cavern can be dotted with tunnel mouths in every wall, in the ceiling, in the floor. When a combat encounter begins in an environment like this, adult kruthiks divide the labor 50/50, half of them immediately moving to engage in melee, the other half hurling spikes while approaching to a distance of 15 to 20 feet. (At more than 20 feet, they can offset the disadvantage incurred by attacking at long range with the advantage they gain from Pack Tactics, but this isn’t ideal. Rather, upon joining the fight, they’ll move toward their target, then attack, and stop advancing only when they’ve reached their ideal range.)
Moreover, while they’re fighting, they’re chittering away in their own language, calling for reinforcements. In an environment like the one I just described, you can have waves of reinforcements pour forth from the tunnels, adding to the number of ranged attackers and maxing out at a ratio of two ranged attackers per melee attacker. If your desired combat difficulty demands even more kruthiks than this, some of the earlier-arriving ranged attackers switch to melee to maintain the 2-to-1 ratio.
Young kruthiks that have the numbers to stand their ground do so only in open areas that allow them to swarm. They’re not necessarily mature enough yet to employ the trick of digging alcoves in a tunnel, waiting for a pursuer to pass by, and attacking him or her from all sides. If you have multiple young kruthiks fleeing down a tunnel—or one fleeing toward other young kruthiks—flip a coin to decide whether each one digs itself a bolthole or just keeps going. If a young kruthik should happen to dig its bolthole where none of its siblings have done the same, it digs as far as it can before its pursuer catches up, then simply Hides and stays still, hoping its pursuer will pass it by.
Even young kruthiks that stand and fight don’t need to take much damage to discourage them. A moderately wounded young kruthik (reduced to 6 hp or fewer) Dodges and retreats, climbing up the nearest wall and burrowing through the ceiling. Adult kruthiks are more tenacious, Dodging and retreating when seriously wounded (reduced to 15 hp or fewer). They use existing tunnels where available and burrow upward through the ceiling otherwise. Retreating kruthiks aren’t intelligent enough to Disengage, even when facing multiple melee opponents, but with their high AC, Dodging will usually suffice.
All this describes the behavior of kruthiks that are defending themselves against intruders. Kruthiks on the hunt behave a little bit differently. Young kruthiks still require 3-to-1 numerical superiority to attack a Medium-size prey creature, 6-to-1 to attack a Large creature, such as a cow. When they reduce their prey to 0 hp, they don’t stop attacking, but rather keep going until it’s dead (technically, they’re still making Stab attacks, but construe these as devouring their freshly killed prey). Adult kruthiks are bolder: if it’s hungry enough, one alone will attack a Medium-size prey creature, although they’ll usually prefer to double-team it, and two are also enough to attack a Large creature. They, too, keep attacking until they’ve picked the bones of their dinner clean. Alternatively, they may reduce it to 0 hp, instinctively making their last attack a nonlethal one, then drag it back into their lair to feed it to their hive lord.
A kruthik hive lord won’t ever be found outside a kruthik nest. Unlike young and adult kruthiks, the hive lord is unambiguously a brute melee fighter. Even though it’s invariably accompanied by a cluster of adult kruthiks acting as soldiers, it doesn’t hang back behind them; it wades right into battle alongside them. Whenever it can, it uses its Acid Spray action to hose down two or more attacking enemies. Otherwise, it defaults to a stab/stab Multiattack.
Unlike other kruthiks, the kruthik hive lord has sufficient Intelligence and Wisdom to recognize when it’s facing extraordinary opposition. Although its default combat mode is melee, it will switch to hurling spikes at opponents using ranged weapons or especially threatening magic, while its soldiers run interference for it. It may even order a couple of those kruthiks to break away from melee to chase down such an opponent, so it can gain advantage from Pack Tactics itself. But it’s also got the horse sense to recognize when it’s hopelessly outmatched and try to parley its way out of a potentially devastating fight. Mind you, this won’t be an easy thing: kruthiks speak only Kruthik, and while they’re not aberrations, their physiology is alien enough to humanoid physiology that it may be extremely difficult to interpret their gestures. But a burst of vocalization, gestures and floor-tapping, followed by a the bodyguard kruthiks’ arranging themselves in a protective formation around their hive lord while also relaxing their combat posture, should be a clear enough message that at least one PC can interpret it correctly. It may even be possible to negotiate a truce if the PCs can credibly pledge to provide a steady source of fresh food and respect for the kruthiks’ territory.
Adult kruthiks in the presence of a kruthik hive lord will fight to the death, if it comes to that, acting as a rearguard while the hive lord Dodges and burrows its way to safety. The hive lord withdraws when it’s seriously wounded (reduced to 40 hp or fewer).
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