Magic: The Gathering's Teenage Mutant Ninja Turtles set highlights a problem where the needs of Universes Beyond crossovers don't gel with the TCG's mechanics. The set's lead, Eric Engelhard, discussed the issue in a recent design article.
It's all to do with the high number of legendary creatures in UB sets like TMNT, in particular, the appearance of legendary creatures at low rarities, which means the Legend Rule (dictating you can only have one copy of a legendary card on the field) rears its head way too often and starts causing some serious deck-building issues.
Universes Beyond sets have always had more legendary creatures than in-universe MTG sets because the franchises they're dedicated to have large numbers of named characters Wizards need to show off.
But until recently, these cards have been restricted to the higher rarities. Spider-Man started a trend of allowing legendary creatures at common, and this has continued with TMNT, where each of the four main characters has a main set card at every rarity, from mythic all the way down to common.
As a result, the density of legendary cards in UB is getting worse. Avatar: The Last Airbender had legends for 76 out of 281 of its main set cards (27%). But 73 out of just 185 TMNT cards are legendary, a whopping 39%! Compare that to Lorwyn Eclipsed, which had just 20 legendary cards out of 268 cards total, and it just seems silly.
The trouble is, Wizards needs to ensure that there are highly recognisable characters, creatures, or for lack of a better term 'things' in every UB booster pack, otherwise it's not doing its job at appealing to fans of the selected franchise.
And, as Engelhard puts it: "Some franchises have plenty of interesting generic concepts that players know, many don't, and TMNT is one of them."
So far, one of Wizards' tactics for reducing the number of legendary cards in UB sets which don't have extensive fantasy worlds like Avatar' and Lord of the Rings' is to give generic names to named side characters. So in TMNT, Alopex became Turncoat Kunoichi, Pigeon Pete became Featherbrained Filcher, and Muckman and Joe Eyeball became Putrid Pals.
But, the set lead explains, Wizards "want recognizable characters at low rarities, and the more recognizable characters can't be non-legendary."
"We couldn't put a picture of Leonardo on a creature card and call it 'Youthful Altered Stealth-Inclined Tortoise'," he points out.
How to solve the quandary, besides not making UB sets that don't have fleshed-out fantasy worlds? (Who said that?) Engelhard, and apparently MTG design head Mark Rosewater, favor removing the requirement for named characters to be legendary.
But while the debate doesn't seem to be over, so far they've been overruled by the majority of R&D, who favor the current approach of genericising some creatures that could've been legendaries and using as many generic creature concepts as possible.
I'm sure you're all wondering, what I, personally, would do. Well, I'm really not a fan of legendaries at common because the legend rule popping up so often makes both constructed and limited gameplay and deckbuilding worse. Engelhard's article says Wizards "can't have 26 legendary commons" but I think the 11 legendary commons they do have is also too many.
So I think Wizards should have leaned hard in either direction to avoid this situation. I'm not sure I agree with the set lead that you couldn't have genericised common versions of more of these characters. Actually, now I am sure. I don't agree.
I can't see an issue with taking the names away from Zog, Tricetron Castaway or Stockman, Mad Fly-entist, especially if you ensured there were legendary versions of these characters at higher rarities. In fact, I'll go further, this would be fine for all of the common legends. You could definitely have a non-legendary card called 'Tough Turtle' with the same artwork of Raphael. That would be fine.
On the other hand, I also don't think it would be the end of the world if Wizards created a new norm that you can have named common cards that aren't legendary. It's not like the legend rule hasn't changed before.
Also, this is something the game has already done for lands. Legendary lands became far less common after Tales from Middle Earth, and named locations regularly appear on Magic cards without the legendary supertype. Did anyone care that the planet lands in Edge of Eternities, like Kavaron, Memorial World weren't legendary? For the most part, no one seems to mind.