That squid-tentacle-looking-individual is a Zygon. They were first seen in 1975 where the fourth doctor defeated their attempt to attack an energy conference. They can shapeshift and have since peacefully relocated to Earth (their own home planet having been destroyed during the Time War). However, they are under a treaty that keeps them from revealing themselves to humans. So you never know, your best friend could be one and you'd never know.
Source