Nintendo

That's my usual strategy - this was the first time I had to do it without really having a reference image. I didn't even try to use what was visible on the box.

It ended up not being too hard. In the beginning (after the edge obviously) I progressed by sorting pieces by color. As an example, I put every single piece with even a tiny bit of purple into one pile. Then I tried to connect the pieces in just that pile - which in the case of purple ended up making me 3 or 4 distinct objects. While I didn't know what I was making (I thought I was making a sea monster, ended up being a straw hat), the pool of pieces was low enough to make it not too hard to find connections.

Once I'd done that for all the colors that were rare enough to make that strategy useful, I was about half-way done - by which point it wasn't too bad to figure out what sorts of pieces I needed to find to extend which sections of puzzle I already had assembled. The only truly painful part was all the pieces that were just water - which would have been hard even with a reference picture.

It can also help to sort the pieces by shape: since there are so many fewer of the non-standard shapes you have a lot fewer pieces to check when you find a missing spot that's not going to to fit a standard piece. And you can get pretty tricky about how you spot where nonstandard pieces go: For example, two innie or two outie bits in a row on an edge mean one of them has to be nonstandard, as do a few other patterns.

The surprise is nice: The puzzle I did ended up being vaguely Christmas themed, which is something you can't tell from the box at all.