100% Question
 

I've seen a handful of people talking about getting the 100% achievement prior to completing all of the Cotton Alley levels. I finished the Light World of Cotton Alley and I'm about halfway through the Dark World.

From what I've read, it looks like people were getting their 100% about halfway through the Dark World. I'm looking forward to rocking all of the Dark World levels, but just curious if anyone can shed some light on this possible glitch? Or am I mistaken altogether? : )

p.s. This game is unreal. I recall being slightly depressed when N+ came to its conclusion. SMB will certainly be no exception.

Its a glitch by cheaters.

I don't think that glitch exists any longer. I currently have 103% overall in the game and got no achievement. Light World is at 100% and Dark World is at 96% or so. I only have 6 of the Dark World levels in Cotton Alley for my full 200.

I will confirm this.. From chapters 1-7 in the light world i collected all bandages, did all warp zones and completed it A+. For the dark world i did the exact same thing except.. it gave me the 100% achievement after completing 7-18x so i was like "oh cool... let me look at my stats for the game" it showed Total progress 100%
Light World 100%
Dark World 98%
i guess the total progress goes over 100% giving you the achievement.

The 100% is an average across all worlds. Since you can get more than 100% in some worlds, you can afford to get less in others. Hence the unlock.

same happened to me except I got 99% on Dark world. it seems like the total progress will be calculated from the average progress of light and dark world.
100+99 = 199
199/2 = 99.5
the game rounds up to 100% and you get the achievement
and after I beat the last two cotton levels I got 103% on cotton alley and had a total progress of 101% :D

In my case the Golden God achievement popped when I had 4 levels left to do in the Cotton Alley Dark World. On statistics it says I have 101% overall :S

I have 101% overall.

Typically I hear of the achievement popping early when people collect a bandage more than once due to the respawning bandage glitch (You pretty much get the bandage but the game doesn't realize it enough to take it out of the stage or mark it off the map.. so it still puts it in the level but also gives you the bandage for your total) which boosts their overall stage completion above 100%.. or at least it used to. I'm almost positive this has been patched now.

So I just popped Golden God achievement with four levels to go in Cotton Alley dark world. My progress shows 101% complete. I only assume this is because of the bonus warp zones uncovered and completed.

Grats to me for 200/2000, but I still plan on finishing the remaining levels.