0.5mm & 1mm plaplate to construct the base & triangle plastic beam to support the 4 sides

Paper clay to create the base, and bought various real stone from aquarium shop...

placing various stones & pour putty+sand on it

same color scheme like i applied on the semi sphere, and also apply some green color on the stones (left pix)
wash the base (not the stones) using enamel brown+black

more views

mecha octopus baby created by koto parts & plastic beam

close up view

just testing for fun, the final one would be:
1 baby octopus stand infront acguy jr.
1 climbing &
1 floating on the water.