@gary-wilkinson What a cool idea! The octopus looks slippery to me already. The surfaces are smooth and curved and the reflection dots achieve this affect. For the water shadows, try Googling pool reflections. You've got the shadow just fine, but that wavy reflective effect that pools create on walls might add to this piece.
The one issue I'm having is that the octopus monster does not feel alive to me. When I first saw it, I thought it was some sort of snow globe, sans the snow. The tentacles also have a plastic or glass feel, rather than a living squirming sea monster. To resolve this, I'd bring those tentacles that are wrapped around the head down and moving around. I'd also spread out the tentacles a bit. I'd also add some monster eyes.