A Boulderkin has a spherical body, with almost comically short legs. They have two to four arms, though the more arms they have the less effective said arms generally are. Boulderkin do not have heads, but rather their faces grow from the front of their boulder like bodies. In terms of size, the average boulderkin is approximately four feet tall (and across) though some have been summoned as large as twelve feet in diameter. Lesser boulderkin have also been summoned, some small enough to be picked up and thrown. THe average Bouldkin weighs approximately 600 pounds, or more. Their mineral composition will mimic whatever the local stone is composed of, and if this stone has any special non-magical properties, the boulderkin in question will share them.
The boulderkin is a naturally occuring stone elemental, frequently encountered in mountainous terrain or underground. As far as elementals go, they are somewhat dull and lacking in intelligence. When given a chance to show off, they like to demonstrate their ability to pointlessly pick up things and move them around. They do not collect anything, have nothing of real value, and lack the discipline for use in construction projects. In the wild, these elementals will be encountered either snoozing like old men at the park, or will be crashing around, rolling down steep cliffs and otherwise generally acting like jack-asses.
With their limited intelligence, Boulderkin are easy to summon, compared to the regular run of the mill humanoid elemental. These bound boulderkin can be put to simple tasks, which they will follow to the best of their ability. If a boulderkin is told to watch a door, it will stare at said door, it might pull the door off its hinges and wander off with it, so caution is in order. Most boulderkin that are summoned are usually summoned for the purpose of combat.
Boulderkin and War
The Boulderkin is not an exceptional soldier, it lacks discipline, cannot follow complex orders, and lacks the normal size associated with war-summonings. But, there is something that Boulderkin are good at, breaking things. When it comes to siege warfare, their single mindedness and destructive tendencies become assets. Given a steep enough hill, they will roll themselves into anything, this is a game to them. The elemental is also not at all adverse to being used as ammunition for siege engines. More than one keep has been broken open by hurling several dozen boulderkin over the wall and into the fortress.
All of the rolling, stone throwing, and other mischief covers one of the most potent of the boulderkin's abilities. A boulderkin can take a second to gather all of its remaining force and then self destruct. This blast shatters their stone husk, filling the air with flying debris, choking dust, and all sorts of chaos. This explosion is not fatal for the elemental, as the are a living essence that animates unliving rock. After a while the same boulderkin can be summoned again, usually 24 hours or so later. The explosion however, can be very fatal for anything close enough to the boulderkin when it detonates. Anything within ten feet of an average sized boulderkin runs the risk of being killed by the forces released by the explosion, with damage from stone debris and such extending out to thirty feet.
Rather than being reluctant about using this ability, boulderkin generally have to be discouraged from detonating at whim. One boulderkin exploding will usually cause the rest of the kin in the general vicinity to also explode, like lemming grenades.