.Mac. said:

It sounds cool to add that large arachnid, but I'm curious where?

Without any new scenes being added to ESB:R (so we've been told) and without it interfering with what's already happening on-screen, the only place that comes to mind where it could work seamlessly is in that wide shot of Luke's X-Wing after he crashes it - you might catch a glimpse of one scampering off-screen to the right. Otherwise, there's honestly no reason to see them.

That is exactly where I thought it could fit. And it seems like a good idea to me, as all we ever see are snakes, lizards, bats, and the "fin" of the water beast. I always thought Dagobah could use more "wildlife" so to speak, to make it feel less like a movie set.

And what better than those arachnids to make Luke think of the planet as creepy? Sure, some people think of snakes and lizards as creepy, but that just seems rather tame for a swamp planet in the Star Wars universe, in my opinion.