Follow these guidelines to get spooky tentacles.
Create a new image any size with a gradient background.(This can also be just one color)
Grab the "Retanguler Marquee Tool" and make a selection kinda like mine:

Fill it with a gradient;
Click Edit>Transform>Perspective and make the gradient look like this:


Click Filter>Disort>Shear and play around with the settings;
Play around with making more tentacles and maybe add some splatters like me:






10 Random Photoshop Drawing Techniques :
10 Random TutorialKit Materials:












More Photoshop: