Okay, so pretty neat thing I've seen in my regular trawl: Wizards of the Coast has published a small free PDF for adapting Dungeons & Dragons rules for gameplay in their Zendikar setting (which is a Magic: The Gathering setting).
There are a few reasons I'm all in for this. One of them is that Zendikar's the Eldrazi setting, and I love Eldrazi. (True story: I've never played Magic, but since the first Mirrodin block I've followed the Daily MTG site on and off because I found I enjoyed reading about the game's mechanical structure and the story and worldbuilding stuff seemed interesting. I stopped reading for a while around Ravnica, because it bored me for reasons I couldn't put my finger on*, checked in a few times without quite getting back into it, then got back into it aggressively when they started doing Rise of the Eldrazi previews. Ahead of even Mirrodin [still my actual favorite MTG setting and one of my all-time favorite fantasy settings] and the Phyrexians [who are hilariously cartoonish gruesome villains and not for the faint of heart; neither are the Eldrazi, for that matter] and Innistrad** and Kamigawa [both fantastically flavorful settings], the Eldrazi are my single favorite thing about MTG.)
Second is that this free PDF seems to be inspired by a lot of ideas I've seen where someone adapts a creature design into another creature using a set of cosmetic changes and some relatively minor ability alterations. This is a fantastic idea and a very useful one (that I've seen thrown around by a lot of D&D fans who homebrew a lot), and seeing it used in an official WoTC document is neat.
...Though I kinda feel the need to call a bit of BS on some of the choices made:
Honestly, part of the problem is that MTG and D&D are differently scaled games from each other, but these are generally "Colossal-sized" creatures, and "Colossal" is a D&D descriptor with some serious problems. Which is to say "MTG 'colossal' is completely different from D&D 'Colossal.'" A "Colossal" creature in D&D can be just 30 feet in one of its dimensions (the PRD for reference; it's effectively a different version of the game published by a different company, but the size categories are probably still about the same***), but a "colossal" MTG creature is something more on the order of big kaiju. (You know those scenes where you can see kaiju towering over bridges? Like that. MTG "colossal" is EFFING MONOLITHIC.) Obviously, everything in D&D is ultimately intended to be hypothetically killable by some guys with nice swords and a bit of magic, and the big Eldrazi, who are definitely big kaiju big, are kinda hard to approach that way.
(Art is a cropped version of the art of Witness the End, which I found on some Daily MTG page I'm not hunting down sometime last year or so.)
D&D has occasionally flirted with monsters on this sort of scale, but only for extremely high-level characters, who are generally essentially physical gods. (For instance, the draeden from BECMI/Mystara, which is something like a thousand miles long and has forty comparably sized tentacles, is immune to mortal-cast spells and will shrug off even Immortal-cast spells 99% of the time, and can cast every mortal spell at will [yes this includes wish go ahead and start crying]. While draedens don't get talked about much in later D&D, there was a reference to a draeden's body actually basically taking up an entire level of the Abyss and its mouth being used as a garbage disposal, which is amazing. Obviously this is a rare case of being much bigger than even the typical MTG "colossal" size, but it's a useful counterexample because it's definitely the exception that proves the rule. The only other major example of a "serious" monster on that scale I can think of is Spelljammer's stellar dragon, which can be millions of miles long, can cast all spells at will and combine or alter other spells or basically invent new ones on the spot, will "only" be completely unaffected by 70% of magic, has a sphere of annihilation in its gut and a tractor beam breath weapon, and can do other stuff that's probably irrelevant because why the hell not at that point these stats only exist to try to terrify you into not picking a fight/tempt you into picking a fight because you're really into Lord British Postulate gaming. And in Spelljammer you'll be meeting this thing while riding a spaceship.) And therein lies a part of the problem: MTG's protagonists, while they're less over-the-top than they used to be, are naturally equivalent to at least very-high-level D&D characters most of the time, and players themselves are still essentially the old-school really ridiculous versions. MTG's kaiju big monsters exist to be cool things for what amount to gods to summon and attack each other with.
Too long, didn't read version: Eldrazi titans would eat the tarrasque for lunch, so at least slap some extra HD on there guys I mean really.
Third, I love seeing intellectual properties being converted to different formats than what they're specifically "intended" for, and a gaming company converting one of its own properties for a different gaming system is such a slam dunk in terms of product synergy that I'm kinda amazed they haven't done this before. (I actually had mentioned this exact subject-that is, using D&D to play MTG settings-to my sister sometime in the last year or two.) It might not take off, but hey, you didn't have to burn money developing a setting or creating a new game, so the development costs are probably just whatever you paid the person who whipped up the PDF.
So I kinda hope to see a bit more of this.
*I eventually did figure out the problem: An ecumenopolis is boring when it's in the context of being the norm. It's only interesting when it has more normal worlds to contrast, and in general Ravnica is basically an extremely isolated ecumenopolis, thanks to the rarity of planar travel in MTG for anyone but planeswalkers. If it was part of a multiverse with more open travel, e.g. Planescape or Spelljammer (to give D&D examples, since I'm on the subject), I'd actually think it was pretty cool.
**Digression: I love Innistrad, but I've been pretty lukewarm so far on Shadows Over Innistrad block. Biggest issue: They killed off Avacyn, perhaps my favorite part of the setting. Why do I love Avacyn? Because she's an angel who's a bit gothy because she was created by a vampire. That's astounding. (Also, she was created by said vampire because he realized that the vampires would have overrun humanity and eventually gone extinct without her influence. In effect, he created an angel to be a sheepdog because he thought the figurative wolves were thinning the figurative herd too much. I love that, too, in a sort of darkly funny way.)
***Assuming 5ED D&D even uses size categories; I've done some admittedly minimal searches and I don't see references to sizes in some of this stuff.