Never found the tentacles. Did explore the cave and the area across the bridge.
The portal thats at the other side of the river via a bridge breaks the game and makes everything in it lose its textures and models as after i exited the area of where it teleported me to i saw a broken play area and no buildings or mobs or anything. Only thing i saw was just grass and the river.
Also there is no way to get Iron.
Edit: Turns out build 12 was either not the Cave update, or the build just didnt have tentacles or Iron.