Panharmonicon,
Everyone who has played Magic the Gathering in the last year has secretly, or publicly, brewed with this card. Be honest, you have! And it sure feels good, sure it's a little slow, but double Enter the Battlefield?!? Yes please!
Personaly I have played this card when it came out in Kaladesh in the janky infinite Thopters deck below:
Thankfully I picked up my Saheeli's cheap before Aether Revolt spoiled the cat combo. The combo worked by landing a decoction module with a panharmonicon, in verrying amounts, so that when Whirling Virtuosa made a Thopter, the ETB triggers would create 3 energy. Sure felt good to pull off, however like all combo focus decks, this was extremely unreliable!
These days the card sees the majority of it's play in the Commander format. I have mine in a Breya combo deck. A quick look at EDHRec tells us that to date, Panharmonicon has been put in 12188 decks!!
Where do you play Panharmonicon? Is the hype on this card over? I'm still believing!!!