What is the complexity of succinct (binary) Nurikabe?
I don't have a proof of NEXP-completeness but I can offer some evidence that succinct Nurikabe isn't in NP and that it can encode computationally difficult problems. Consider this 17 x 16 Nurikabe puzzle:
and its (I believe) unique solution:
This puzzle is based on the fourth iteration of the Hilbert curve construction described in the Wikipedia article on space filling curves, modified slightly to produce a puzzle with a unique solution. I don't see any way to encode a certificate for this solution with fewer than the 272 bits of the naive encoding. And I don't see any way to solve the puzzle short of exponential trial and error.