This game wasn't released - it escaped!
The premise is the same, and so is the action - jump on enemies to defeat them, collect magic mushrooms (not that kind) to power up and so on. The difficulty however, far from being the simple, yet gently challenging affair of its predecessor, wasn't so much a steep learning curve, as practically vertical!
Pipes that looked harmless would sprout a piranha plant the second you jumped on them, Lakitu would be a constant menace on more levels than are fair or just, some jumps would be just impossible - literally - and with no way to backtrack through levels, an almost inexhaustible amount of lives (and patience) is required to get anywhere with the game.
It gets much worse, with warp zones merrily taking you backwards instead of forwards, meaning you'd have to replay savage levels you swore and cursed and cried your way through over again. Other times there'd be no warp at all, just pipes infested with piranha plants. The sadistic "balance" of luck and perseverance required to beat the game means only real die-hard fans or total masochists will stick this, and even then, fittingly I might add, there is no end, you just start all over again, repeating the same bitter cycle.
This is like playing Resident Evil 5 armed only with a toothpick, and Capcom had the good sense to leave that out. It's easy to understand why us Westerners were given the more sensitive Super Marios Bros. 2 as opposed to this torture. If it's a challenge you want, I can't think of a tougher, harder, more repetitive game than this.