Its a beautifully designed engine that solves the 5-color mana issue by letting you play a Mono-Red game early and a WUBRG game late
We accomplished this by designing a couple cards that really pushed the boundaries of how many creature tokens a single card could make

Abandon Attachments Abstract Paintmage Adeliz, the Cinder Wind Aegar, the Freezing Flame Aetherwing, Golden-Scale Flagship Alania, Divergent Storm Ant-Man, Elusive Avenger Arcane Infusion Arjun, the Shifting Flame Armor Wars Ashling's Command Astonishing Spider-Man Balmor, Battlemage Captain Baral and Kari Zev Battle of Frost and Fire Baxter Stockman Beacon Bolt Beamsplitter Mage Bilbo, Retired Burglar Blast of Genius Blistercoil Weird Bloodwater Entity Boosted Sloop Breeches, the Blastmaker Bria, Riptide Rogue Brilliance Unleashed Broadside Barrage Brudiclad, Telchor Engineer Brutal Expulsion Bucket List (playtest) Call the Skybreaker Captain Howler, Sea Scourge Captain Storm, Cosmium Raider Captain Vargus Wrath Catch // Release Cerebral Vortex Channeled Force Chaos Mutation Chemister's Trick Clout of the Dominus Cloven Casting Collected Conjuring Colorstorm Stallion Compleated Conjurer Corporeal Projection Counterflux Crackleburr Crackling Drake Crag Puca Creative Outburst Cryptic Pursuit Culmination of Studies Cunning Strike Cutthroat Negotiator Cyclops Superconductor Dack Fayden Dack's Duplicate Dalakos, Crafter of Wonders Detective's Satchel Djinn Illuminatus Dominus of Fealty Don & Raph, Hard Science Double Negative Dracoplasm Dragonfly Swarm Dragonshift Eclipsed Flamekin Ecstatic Electromancer Effortless Master Electrolyze Electrosiphon Elemental Expressionist

(Xyz Materials on that monster also become Xyz Materials on this card.) When this card is Xyz summoned, you may Special Summon 1 level 5 or higher LIGHT monster from your deck to your side of the field
Synchro Summons and Link Monsters might get more attention in the meta game, but Fusion is still a good strategy for a strong offense
FORBIDDEN TREASURE At the end of your turn, put all the cards in your hand on the bottom of your deck in any order