The perfect stallion song had multiple one-offs

waffle911: Many folks, both at DHX and Hasbro, already know of Fighting is Magic and many other fan projects, so here's my theory as to why yours got singled out. I think Hasbro's biggest concern here was not the infringement of MLP trademarks, but the potential loss of profit from folks playing their game with non-official cards that were not purchased from Wot C—which is an infringement on the Mt G trademarks, which are very likely under an entirely different set of corporate rules from the MLP IP due to the differences in medium, marketing, distribution, the grounds of the IP, and the different ways in which the Mt G franchise can be infringed upon and exploited. They don't want folks playing their card game (the the game play mechanics, rule sets, and derivations thereof, in whole or in part) for free—which is what Shards of Equestria would allow for—because Wot C and Hasbro have invested a lot of money into the game's development. Fighting is Magic, My Little Investigations, and even Master Age's MLPCCG, however, do not use any Hasbro properties in any way, shape, or form that circumvent the purchase and use of existing Hasbro products, since they are all novel applications with no Hasbro-sanctioned alternatives. Sure, they don't make official MLP-themed Mt G cards, but they do still make Mt G cards, and they expect people to make purchases in order to play their game.

It's not even a matter of whether or not you make any money off it; it's a matter of them not making money. While your project might seem like small potatoes in the grand scheme of things, put it was much more likely to gain traction than many other fan-made card set projects; it's more of a slippery slope where if they allow one such project to go through like this, it opens the door for others like it, including commercially produced sets by third-party companies…partially as a result of trademark and copyright laws both in the U.S. and abroad. And if everyone were to start making their own Mt G sets rather than buying official Wot C sets, then where would that leave them? Not to mention, there's no way they could sanction or support the use of third-party sets within the existing game because there's no way to ensure that cards are balanced according to their extensive (and proprietary) card design policies.

Mind you, people do play with real Mt G card sets illegally over the internet; but the whole way that works out makes it a bit harder for Hasbro to decisively act upon it, as it's a bit more of a distributed effort without any key folks to be able to target. What's more, and partially because they do use official card sets, the folks who enable such activities put in place many non-enforceable policies in usage agreements that are just enough to at least partially absolve themselves of liability for the way their handiwork is used by others. It makes for a relatively flimsy legal barrier to be sure, but it's a barrier nonetheless; and, when combined with the relatively small pool of players who partake in Mt G illegally (for now), it poses enough legal resistance that it currently isn't worth the time and effort of Hasbro's legal team to pursue. You however are one entity that can be singled out, and due to the very nature of Shards of Equestria as an unofficial expansion, many of those flimsy end-user policies wouldn't be applicable to what you were doing. As a result, Hasbro's legal team wouldn't have to do much at all to nip this in the bud.

This is just the way I'm seeing things here and now. Someone else might be able to point out a few flaws with my reasoning, or might have more legal information or expertise to refute anything I've said.