@Geoffrey-Mégardon I know, you are already very far in the progress - I'm sorry I didn't find the time to read through your thread earlier!
I am missing a visual connection between the tentacles and the space ranger. Having them so dark and blueish they more look like a foreground element to me than something that is a danger to him.
How do you think about letting ONE of the tentacles creep on the ground to his feet and touch one of his shoes? This would connect the fore- and the middleground.