2 questions

How do I create a master controller armature ie: one that would move all of the tentacles on a octopus. What is the IK solver?

An IK-Solver is the Target (an Empty, Object or Bone) that the IK-Constraint will use to constrain the rotation of a chain of bones to. It’s also (become) old jargon that was used pre 2.40. Now it an IK-Constraint and its Target.

If I had to do it I would make each tenticle an IK-Chain and use Action Constraints.
Either have a loose or seperate bone drive the actions assigned to all tenticles, or set up the inside bone of each tenticle with an Action Constraint and then set a driver from there to the seperate bone. Actually, on secon thoughts I’d probably just bite the bullet and pose each tenticle seperately, after having much fun with Slow Parent and SoftBodies.

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How do I do that?

Here is a tutorial I wrote out a while back:
http://www.blenderprojects.com/calvin/IK/

Since then I learned that you can create a chain of bones, by simply selecting the first bone and Ctrl+LeftMouseButton click on the screen. Also another thing I did not mention in the tutorial is that the IK bone should not be a child of any bone within the chain and should not be contected to the chain (disabled CO, remove childhood.)

In your case you want one bone to control severval IK bones of different chains. What you can do is simply create another bone, call it master. And parent all the IK bones to it. Go to edit mode, select your IK bone, find the place where it says “Child of” and select master. (Don’t CO.) Now when you move that one bone all the other bones move along.

Is up & downs still alive?