It lets you add a free extra Energy during your turn, whether they are Active or on the bench
Power level wise the card fits in just right in Modern, as there are a lot of threats which go under the card, and cards like Veil of Summer and Cavern of Souls give slower creature/combo decks enough counterplay against it
Mark Rosewater has gone into elaborate detail on double-faced cards on his Drive to Work podcast - I would recommend checking this one out for the history of the mechanic
All War of the Spark Promos cardsMost valuable Magic: The Gathering cards Most valuable cards in War of the Spark Promos 1 Liliana, Dreadhorde General$1,627.36 mythic 2 Narset, Parter of Veils$571.82 uncommon 3 Nissa, Who Shakes the World$389.90 rare 4 Teferi, Time Raveler$277.16 rare 5 Karn, the Great Creator$275.39 rare 6 Gideon Blackblade$249.99 mythic 7 Nicol Bolas, Dragon-God$191.39 mythic 8 Sorin, Vengeful Bloodlord$148.93 rare 9 Chandra, Fire Artisan$137.61 rare 10 Jace, Wielder of Mysteries$128.99 rare Card prices for War of the Spark Promos Track your collection, check card prices, create proxies, and more
Letting one fusion summon a Metalfoe monster and being searchable is all one needs for a good archetype specific fusion spell
The nice thing about this set compared to Obsidian Flames is, that this does have 3 Japanese sets mixed in, with Obsidian Flames this was only 1 set
