Start by applying a nice gradient to the background layer.
Create some circle shapes using elliptical shape tool.
Create more circles spreading out of the image bounds.
Select and merge all the circle layers. Change the layer mode to luminosity.
Similarly create some more circles. Merge and change the layer mode to multiply for this layer.
Create a star shape using polygon shape tool. Apply settings as shown below.
Change the layer mode to "overlay".
Create more duplicates of this layer. With each duplicate layer rotate by few degrees and move as shown below.
Similarly create a series of smaller star shape.
Create some tentacle shapes using pen tool. Change the layer mode to "Difference".
Duplicate layer twice and change the shapes slightly in random fashion.
Open animation window. For the first frame hide all the star shape layers. Keep only original tentacle layer visible. move the circle layer towards the right edge of the file so that all extra circles are there beyond the left edge.
Duplicate frame. Move the circles layer towards right.
Click tween button from animation window. Apply settings as shown.
Now we have a total of 22 frames. To animate tentacles we'll leave them as it is in 1st frame, unhide 2nd position of tentacles in 2nd frame and hide the previous position layer. Similarly for the third frame unhide the 3rd tentacle layer and hide rest of them.
These steps should be repeated every three frames.
As mentioned above unhide the star layers too in sequential frames.
Press Ctrl+Alt+Shift+S to save an optimized animated GIF.
