You're infringing copyright just by using the same characters/names. An ASCII-based game with the same characters/names would also draw the attention of a cease-and-desist.
The more money behind a brand the more likely a cease-and-desist is.
I operate on the expectation that a big branded property has interns which do nothing but look for copyright infringement. So it's not "lawyers" I would worry about avoiding but unpaid student interns with too much time on their hand who want to look good to their bosses so that they might have a chance at working for one of these companies some day.
If you're going to go to the effort of being able to quickly rebrand the game to something safe, personally, I suggest the public version you release -- along with assorted promotional material/websites -- focus on the safe version.
That is, you have a legal game that has an option -- ideally handled by a separate download which can be yanked without disrupting your main site -- which turns it in to a copyright violator. That would allow you to hang your hat on a legal product, but still share the copyright-violating add-on with direct friends/family.
Copyright violation is serious business in the US. It is such a serious business in the US, when big media feels someone overseas violates US copyright, they work to get the person extradited to the US and charged in a US court even though the "crime" never happened in the US.
All you need is for Nintendo to claim they "lost sales" because of your copyright infringement for the cease-and-desist to very quickly include polite requests for money and lawyer fees as well.
As my instructor at school regularly reminded us: C.Y.A. (Cover Your Ass/Arse).
Also note: If you're putting up something which violates copyright you will probably be violating your agreement with your ISP and whatever host you're using to store the thing. Unless you're hosting it on your own hardware expect all access to your service provider to be shut down and never brought back up. If you're hosting it on your own hardware you may still be violating your ISP's usage policy and could be blacklisted from ever using that ISP ever again.
For instance,
http://www.google.com/intl/en/policies/terms/ lists "We respond to notices of alleged copyright infringement and terminate accounts of repeat infringers according to the process set out in the U.S. Digital Millennium Copyright Act." I would expect the lawyers involved on the opposition side to be very punctual with regards to timing and to actively hope they'll be able to get you terminated.
So... this means you're potentially looking forward to getting a cease-and-desist while you're on a vacation somewhere without Internet access, then have your services all terminated because you didn't respond fast enough. -- This is what could happen to you if you accept the risk of a cease-and-desist.
Cheers,
Steven Black
