Is the beast Cthulu?

Cthulhu isn't _covered_ with tentacles so I wouldn't think so. Probably just some big generic monstrosity.

While these options clearly refer to certain beings with godlike powers, the questions doesn't actually say that you are those beings or have their powers.

When I simply look at the options as given, I have to go with the tentacled beast. At least a tentacled beast is guaranteed to be able to move around and affect its environment. With the eye, all its guaranteed to be able to do is blink and be on fire.

Sure, they probably both have other amazing powers, but there is no guarantee, which is why, in the absence of any further data, I pick the tentacled beast.

Sorry jonny... no one said anything about eyelids.

But you are correct, there is very little to go off of. The flaming eye could be part of the gigantic beast.
Or the beast is blind.

Is this a slow thing?

I get the impression that it happens suddenly at the end of a 10 year reprieve with this one. There's another option floating around that explicitly says "the thing this is paired with happens slowly over 10 years."