Pachinko Machine seems to be workable as long as you don't input anything when Mario gets launched from the trampoline, iirc. The poison river, though, the level itself is not too hard, it's just accessing it is a demonstration of stunning incompetent design. You had to board a slow boat due to Yoshi dissolving in water, and if you miss a red coin in the level itself and take the pipe exit, which warps you SOMEHOW not to the entrance of the stage but in the Isle Delfino main plaza, you have to do that whole process all over.
My own beloathed level is the roller coaster one because it requires precision aiming when the way that shooting is designed is far from precise. Sure, it works fine shooting crap at Mecha Bowser, but NOT with balloon targets. You also fail the mission, you die for some reason.
The Secret of the Dirty Lake red coins was just plain difficult but that may be just from my experience using the Rocket Nozzle. IDK.