
The first two acts are one giant death trap from start to finish.

Even Sonic Team thought that was too harsh! It could've been worse - the original level order was to have Labyrinth Zone right after Green Hill.

Despite the fact there's no "real" boss battle in the Labyrinth Zone, there are traps strewn about, wasting Sonic's time as he deals with rising water and not a ring in sight while chasing after Robotnik/Eggman. The maze-like designs in both Acts 2 and 3 certainly seal this level's fate for this trope.

TVTROPES SONIC MANIA FULL
Not only it is full of traps and tough obstacles, but it comes right after Green Hill Zone, which is much faster paced compared to this one. The Marble Zone can be hard to some players.
