What are the difference between Koro-sensei and other tentacle creatures? Koro-sensei and tentacle-having humans (e.g. Itona) have a drastic difference in their bodies: Koro-sensei's body is made up of tentacles wholly, whereas Itona has his human body along with a tentacle.

Are there any differences between the no. of the tentacle cells infused? If yes, it's a fact that even a single tentacle cell can cause death like pain, then how did Koro-sensei survive that much pain?
The most important point is that Koro-sensei told his tentacles that he doesn't want to be powerful, so they became like they now look.

The other tentacle monsters only wanted power and told the tentacles, so their tentacles became hard and strong.