You summon a Vrock that appears in an unoccupied space you can see within range. The Vrock's disappears when it drops to 0 hit points or when the spell ends.   The Vrock’s attitude depends on the value of the gem used as a material component for this spell. Roll initiative for the Vrock, which has its own turns. At the start of the Vrock’s turn, the DM makes a secret Charisma check on your behalf, with a bonus equal to the gem’s value divided by 20. The check DC starts at 10 and increases by 2 each round. You can issue orders to the Vrock and have it obey you as long as you succeed on the Charisma check.   If the check fails, the spell no longer requires concentration and the Vrock is no longer under your control. The Vrock takes no actions on its next turn and uses its telepathy to tell any creature it can see that it will fight in exchange for treasure. The creature that gives the Vrock the most expensive gem can command it for the next 1d6 rounds. At the end of that time, it offers the bargain again. If no one offers the Vrock treasure before its next turn begins, it attacks the nearest creatures for 1d6 rounds before returning to the Abyss.   As part of casting the spell, you can scribe a circle on the ground using the blood of an intelligent humanoid slain within the past 24 hours. The circle is large enough to encompass your space. The summoned Vrock cannot cross the circle or target anyone in it while the spell lasts.