During Wonder-Pink's introduction, Wonder Blue refers to the spiky Gedie Dough-Goo they were dealing at the time as a "pain in the butt hedgehog".
In the scene where Vijounne and Pink are throwing profane insults at one another, Vijounne calls Pink a "ditzy, cheerleader-looking, pom-pom-headed [BLEEP]". This is a reference to Pink's English voice actor, Tara Strong, also voicing zombie-hunting cheerleader Juliet Starling.
Colbert Bump: Music and main Wonderful One trophies featured in Super Smash Bros for the Wii U have helped give this game attention (and helped convince unsure people it's a first party Nintendo title).
Screwed by the Network: Nintendo gave this game very little marketing outside of Japan and then shipped thirty-thousand units in Japan alone. After about 5,000 units in one day of Japanese sales, the game went to sell near 3,500 more in the following week since launch, almost clearing a third of the initial shipment of units.
The game is doing even worse in Europe, only selling about 7,000 units after one week of sales.
In America, it shared the same fate as in Japan and Europe with 15,000 units after one week of sales. It didn't help that Nintendo of America made the ridiculous decision of releasing it two days before Grand Theft Auto V, and that initial shipments to stores were as slim as or slimmer than Japan's initial shipments. Even worse is the fact that Nintendo keeps trying to push eShop purchases rather than retail, and gave the game no television ads whatsoever (although it did get quite a bit of online advertising). As such, the game has been selling a lot better digitally than retail-wise.
What Could Have Been: The original product proposal was for the game to be a sister series to Super Smash Bros. with 100 playable Nintendo characters at once. It was also going to have a darker artstyle rather than a colorful and cutesy artstyle.
According to Kamiya's tweets, Platinum approached Nintendo asking if the Punch-Out!! theme could be used in Operation 5-C, but Nintendo declined their request.