Harpocrates

Harpocrates was the Ptolemaic god of Silence and was responsible for the communication trouble the demigods were having.

The Tyrant's Tomb
Harpocrates was imprisoned by The Triumvirate and forced to silence communications for the demigods. He was eventually freed by Apollo, Reyna, and Meg before he passed away willingly.

Abilities

 * Silence: Harpocrates is able to induce silence around him, those that get to close to him are unable to speak. Once imprisoned his powers were amplified silencing communications for demigods.