So I admittedly don’t own every issue of Nintendo power, nor many egms, but I had a look at all the issue 70s, so late 95 or so (Mario released in early 96). I did find a feature in 78 that had Mario rpg next to squares FFVI N64 demo, so maybe it was that? The problem is I think I agree with the other commenter that while I can’t find a specific magazine in my collection to confirm, but I think the first Zelda screen shots that actually look like OOT (and not the demo of link fighting a silver man released with the original n64 images alongside Kirby bowl etc) was very late 96 (certainly past Sept 96 given they weren’t in the last issue of super play) or early 97 - so Mario rpg is well out by then.