Less than a month ago, I wrote this:
[My Little Pony: Fighting is Magic] also seems like exactly the kind of thing that would eventually draw a Cease & Desist letter from Hasbro's corporate lawyers.
And while I wouldn't necessarily blame Hasbro for that – my own understanding of US trademark law, which is probably off because I'm neither a legal professional nor from the USA to begin with, is that they are required to protect their trademarks so they won't possibly lose them, e.g. when a defendant in a hypothetical future lawsuit points to violations that Hasbro knew but did not do anything about –, it does highlight one of the problems with being a fan of something that is, ultimately, controlled by a for-profit corporation.
(And the whole thing's far from hypothetical, too, as evidenced by the C&D letters sent to e.g. WhiteDove, previously known for her high-quality plushies (even Lauren Faust herself got one!), Shards of Equestria (an MLP:FiM take on M:tG), MLP: Online (an MMO game) and so on.
Hasbro probably know about Fighting is Magic but doesn't consider it to have reached the point where they cannot plausibly deny doing so anymore, but once there's an actual release (there hasn't been one yet), who knows how much longer this'll last.
We have received a C&D letter from Hasbro's Legal representatives, asking us to cease game development, remove any materials that might contain My Little Pony characters, names, locations or related elements from the sites we control (Our site, our youtube, our twitch), and "cease any further use of [their] MY LITTLE PONY property".
Options have been considered, lawyers have been contacted, and resources have been (mostly) exhausted.
We have attempted negotiating with Hasbro for the continued use of the property in our non-profit, voluntary project, but so far we haven't received an answer. As such, we're complying with the contents of the C&D letter until we receive answer from their PR and/or Legal departments.
Fighting is Magic got some press earlier this year when it was nominated as a possible EVO 2013 game; one wonders whether this caused Hasbro to reach the point where they felt they could not plausibly deny being aware of it anymore.
The whole thing isn't quite over; the Mane Six have been trying to get in touch with Hasbro, as noted above, and Lauren Faust herself has offered help in the form of original characters for a new fighting game. It won't be ponies, one presumes, but anything created by Lauren is sure to be good.
Either way, though, the whole thing illustrates the precariousness of being a fan of a corporate-controlled franchise. All in all, I think Hasbro has been dealing with bronies admirably, and I'm sure they didn't do this without regard for the Fighting is Magic developers, but it drives home again how every pretty much every fan project or endeavour exists under a sword of Damocles — and the higher the profile, the thinner the thread.
EDIT: EqD editorial.