The Meaning of Life, the Universe, and Everything.
The anthropophagus bush is a jungle bush, but missing the wood in the centre, but doesn't decay. In the cavity, there is a neutral mob which does not despawn. It looks like a squid with bark skin and pure red glowing eyes. It has high health, high defence and high attack. It can fly, change size up to 150 blocks high and open doors. It attacks villagers if they are present, and illagers if they are present, but no villagers are. If no villagers/illagers are present it is hostile. It heals when it attacks.
I'm very confused by this suggestion. From what I can gather, some bushes in jungle biomes would actually be an unnamed neutral mob that never despawns. It would be incredibly powerful and have no weaknesses. It heals when it attacks. Oh, and it could grow to 150 blocks tall. And it looks like a squid.
The vagueness of this suggestion makes it impossible to understand. This mob doesn't even have a name. While you might have a detailed idea in your head, we can't read your mind. All we know is what you write in your OP.
As for the idea, it's hilariously overpowered (heals when it attacks? 150 blocks tall?). No one would ever go to jungles anymore with these roaming around. It never despawning would cause an extreme amount of lag.