The black sheep among Super Mario brothers, Super Mario Bros. 2 was a quirky side-adventure that featured strange new enemies - an egg-spitting pink anteater, a mouse with a penchant for bombs and sunglasses, and a giant king toad among them - as well as new music and new styles of gameplay (with Mario and co. no longer confined to explore pipes and horizontal planes; now there are pots to comb and vertical terraces to climb). Super Mario Bros. 2 was just... different.
The original sequel to Super Mario Bros. was released in Japan two years prior, but wasn't released in the west until 1993 (included in the Super Mario All-Stars collection as The Lost Levels). What was published in North America as Super Mario Bros. 2 was actually a re-branding of the Japanese game Yume Kojo: Doki Doki Panic (literally, "Dream Factory: Heart-Pounding Panic"), a platformer with an Arabian setting released for the Famicom Disc System.
The Japanese version of SMB2 was directed by Takashi Tezuka. Visually, it looked almost exactly like the original Super Mario Bros. It even retained the same same objective. The level of difficulty, which was increased, was the only significant change.
Nintendo of America disliked the Japanese Super Mario Bros. 2, which they found to be frustratingly difficult and otherwise little more than a modification of Super Mario Bros. NOA canceled the stateside release and looked for an alternative, which they found in Doki Doki Panic, a game Shigeru Miyamoto (director of the original SMB) actually put more time into than the sequel.
Doki Doki Panic was a platforming game that followed a family of four, each with different abilities, on a quest to rescue kidnapped children in a strange fantasy land. Mario, Luigi, Peach, and Toad were built on the character models of Brother, Mama, Sister, and Papa, respectively, marking the first time that Mario and Luigi had noticeably different heights. Some elements from the Mario universe already existed in Doki Doki Panic, such as Starmen, coin and jumping sound effects, the POW blocks and level warping.1