Concepts of Roteye’s dire gargoyle.
The general idea is that the thing is bound to him and will only listen to his commands and answer his call only, unless there’s a more powerful death knight that can subdue it. The gargoyle has runes on its body, similar to his, and is basically something like a deathcharger’s spirit – bound to a trinket, but can turn into a creature of “flesh and blood” when summoned. Calling it requires to perform a simple ritual that involves several ingredients, including fresh blood.