The tentacle are those three green things that come out of the floor, attacked a poor scientist, kept banging on the floor, was a pain to kill (you had to turn on 2 switches from 2 sides of the map!), and was blind. Other than his looks changing, you were originally supposed to enter the room he is on the ground floor and watch him come out from there, and a Barney is there too!
Him coming out from a first floor perspective with a Barney watching
Notice how he sort of looked like a saw where he would cut you instead of crushing you like he does currently.
It does look cool from a first floor perspective though!