The announcement post on the Isaac blog describes Bum-bo as, “a turn-based puzzle RPG type thingy thats [sic] randomly generated.” McMillen acknowledged the significance of announcing the game there, implying that Bum-bo will have some sort of connection to The Binding of Isaac. The coin and turd pile in the logo image included with the announcement are two of the most frequently recurring items in that previous game, corroborating that implication.
In The Binding of Isaac, Bumbo is a collectible power-up added in the recent Afterbirth expansion. It starts as the disembodied head of one of the beggars that occasionally pop up in the game’s randomly generated levels, floating around with Isaac and collecting coins which it consumes to level up and gain new attack abilities that aid Isaac. The “Bum-bo want coin!” slogan in the announcement logo thus suggests that this is likely the same character. Id and McMillen both retweeted an image from artist Tikara, who has created artwork for official Isaac merchandise.
Bumbo finally got coin… now Bumbo want ADVENTURE! @edmundmcmillen @jamesid pic.twitter.com/ZTygMXCt1y
— Tikara (R.C) (@TikaratheMew) March 22, 2016
First released in 2011, The Binding of Isaac is an action rogue-like game loosely inspired by the Biblical episode of the same name. Isaac is a young boy whose fanatical mother believes that God ordered her to kill him as a test of faith. He escapes into the basement and must descend through a series of procedurally generated levels inspired by dungeons from the original Legend of Zelda, shooting tears as a weapon. An enormous number of power-ups can be found to enhance Isaac’s abilities in ways ranging from subtle to completely absurd.
The game mixes challenging arcade gameplay with grotesque imagery and religious iconography in a uniquely personal cocktail. Despite its theologically offensive nature, it has been massively successful, receiving a series of ports and updates up to as recently as October 2015 with the Afterbirth expansion.