As a thin plumber, I think some of the levels aren't as wide as they should be

[MarioSMB]

Each of the levels (including their sub areas) should be a width of 5 blocks. Some aren't following this standard yet...
5 blocks allows the main level geometry plus some back and front scene stuff (like bush), and provides some more 3 dimensional look to the levels.

[z]

• [x] 4-2
• [x] 5-1
• [x] 5-2
• [x] 5-3
• [x] 6-1
• [x] 6-2
• [x] 7-1
• [x] 7-2
• [x] 7-3
• [x] 8-1
• [x] 8-4
• [x] -1
• [x] -2
• [x] -3

[z]

^ meant #25 an #26