OK, we literally just heard news of a court case where the judge specifically said you cannot copyright game mechanics and gameplay type stuff—if I recall correctly, the article was posted on this very site about a week or two ago—and the only thing this game looks to have in common with those other game examples is some general gameplay stuff. So, there's something very amiss with Nintendo threatening to not let this guy keep his game on the store. I'd file some kind of reverse legal action here for abuse of their position or whatever, both against Nintendo and the other publisher. This guy appears to be well within his rights here, and Nintendo should not be threatening him with removal of his game unless the publisher can show some legal right it has to make such a demand. This is just a couple of corporate giants playing ball with each other at the expense of the little guy, who, from where I'm standing, looks to have done nothing wrong.

Edit: Here's that article:

https://www.nintendolife.com/news/2016/06/texas_court_ruling_states_that_game_mechanics_cant_be_protected_by_copyright

Also, he doesn't necessarily need to spend money to fight them. Go to citizens advice or whatever and get some free legal advice on what your options are, and maybe see if you can even get free legal representation or whatever options are available. Don't allow them to do exactly what they're trying to do, which is to get you to give up and lose by default simply because you think you don't have any options to do otherwise. That is exactly how these big corporations get away with much of the crap they get away with on a daily basis; they basically play the odds because they've little to lose in most cases as most people give up at the drop of a hat.

Warner Bros. tried this kind of crap with me regarding my company name/logo, and in 99% of cases they'd have won just because the other side would have given up out of sheer fear, but I didn't give up. I was a stubborn git who refused to quit—you guys know what I'm like when I get my back up about something—and I also made sure I did everything myself so I didn't have to pay a stinking lawyer. In the end Warner Bros. gave in, because they knew their initial case was just chancing its luck in the first place and they also saw that I wasn't going away, and every day the case went on they were spending hundreds/thousands of dollars on douche lawyers and I was spending nothing. So, who do you imagine was going to hold out the longest in such a scenario (as "negotiations" dragged on and on, for two years)?

These corporate giants aren't untouchable, and if you don't think you've done anything wrong—and don't believe you have done something wrong just because they say you have (they're always gonna make that claim)—then stand your ground and fight for you rights (just do so very smartly and within your means and limitations).