
It has a silly name, it feels unoriginal, and it had worse gameplay than Morph-Megamorph creatures had smaller stats than morph creatures, making them worse to play face up, or had substantially higher megamorph costs, making their versatility less relevant.
The last section aside, I’m by no means surprised by Megamorph’s unpopularity. There’s more than just power, versatility, and comprehensibility to a mechanic’s success or failure.
As for comprehensibility, Megamorph is just about as complicated as Morph and arguably more complicated then Manifest, but it scores far worse. In Limited, it had some of the best commons (Misthoof Kirin, Ojutai Interceptor, Atarka Efreet, and Aerie Bowmasters, making the mechanic visible to and powerful for Limited aficionados. It has a cycle of incredibly powerful Standard/Cube cards: Hidden Dragonslayer, Stratus Dancer, Silumgar Assassin, Ire Shaman, and chief above all, Den Protector, in addition to Deathmist Raptor, Ainok Survivalist, and Shorecrasher Elemental. Megamorph seems to succeed in all three categories. Whether it’s relevant in Constructed and Limited. However, popularity seems to usually be linked to three factors: Popularity is clearly a major factor in a mechanic’s likelihood to return.