Sonic Robo Blast 2: Unlocking the hidden Eggman door in Deep Sea Zone Act 1

Within v2.2's iteration of Deep Sea Zone Act 1, there rests a door hidden behind the level's exit accessible from a hidden bustable block atop the tower. The door is closed by default, but by opening all three doors that lead to the signpost (an emblem challenge in of itself) and navigating back to the clover emblem's room near the beginning, a hidden room is unlocked where you can press a button to open the door. Behind it is some nice art of v2.2's final boss, Black Eggman! This is the only point before Black Core Zone Act 3 where you would be able to see him, so that's notable at least.

Why is this here, you may ask? While it seems like just a clever button hunt and easter egg (which it is!), there's a deeper explanation behind its placement. During v2.2's development, many stages were not entirely finished being revamped. To get the update out at a reasonable pace (5 years, as it was between v2.0 and v2.1), many concepts and ideas were abandoned. This includes Red Volcano Zone's elusive second and third act, as well as Egg Rock Zone's ground-up remake which wasn't finished after the earlier remake seen in 2018 was scrapped. More importantly, however, many existing stages were left in partially finished states - this Black Eggman texture is used in multiple other places in v2.2, including in both acts of Techno Hill Zone and notably Castle Eggman Zone Act 2, to denote unfinished areas in which future expansions are planned. This likely means whatever was supposed to be here was never finished, but at least we get a cool portrait!