As part of its ongoing efforts to promote every single Pokémon out there, The Pokémon Company has shared special content dedicated to Tentacruel:
Did you know? It fires off ultrasonic waves from its red orbs to weaken its prey, and then it wraps them up in its 80 tentacles. It communicates with others of its kind by lighting up the red orbs on its head. When the orbs are blinking, it’s a warning sign.
Source: The Pokémon Company