Here is a Minoan octopus vase.
Late Bronze Age Mycenean vase
About the same time, the Mycenaeans also began painting creamy backgrounds with pictures of real things (as in the earlier Dimini period), but the Mycenaeans mainly didn't choose ocean creatures. They painted horses, chariots, men and women instead.
In the end of the Mycenean period, after the Greeks had conquered Crete, Mycenean potters began to imitate Minoan (Cretan) pottery styles. But when the Mycenaeans copied Minoan octopus pots, they painted the octopus much stiffer and more symmetrical, much less wild than the Minoan ones (and not looking so much like octopuses or seaweed). That's the same attitude that Mycenaean painters doing frescoes in the palaces showed too.
A later octopus vase
An even later octopus vase
Towards the end of the Late Bronze Age, the octopuses got simpler and simpler, and more and more abstract. During the Greek Dark Ages, Greek artists painted the octopus just as one long wavy horizontal line around the middle of their vase.
Learn by doing: draw your own octopus
More about Sub-Mycenaean (Dark Age) pottery
The Archaeology of Greece: An Introduction, by William R. Biers (1996). Biers writes very clearly and has a lot of good pictures.
Greek Art and Archaeology (3rd Edition), by John G. Pedley (2002) This has a lot of good information and is pretty readable. Plus, the author is really an expert in this field.
The Aegean Bronze Age (Cambridge World Archaeology) by Oliver Dickinson, Norman Yoffee (Editor) (1994)
Minoan and Mycenaean Art, by Reynold Higgins (2nd revised edition 1997) The standard book for college students.