We havent gotten all of the mythics yet, but weve gotten a peek at Battles
You can also pour infinite mana through Memnarch to take everything your opponents own
Serah Farron's last ability checks at the moment it would trigger to see if you control two or more other legendary creatures
Beyond this the synergies are subtle and tend to only involve a few cards, for example Chandra's Phoenix improves Lava Dart, the few creature pump effects improve Spikeshot Elder, Mogg Fanatic and other creature sacrifice effects improve Brimstone Volley and the things that give haste work really well with Keldon Marauders
Shadow of the Second Sun is huge here, as you can get your commanders benefit right after casting the Shadow, as is Portal to Phyrexia to undo whatever benefits your opponents obtained
Saga Creatures FINAL FANTASY's classic summons are ready to hit the battlefield in the form of Saga creatures