Some random tips:

• In Area 3, to get to the Jump Booster dungeon you have to hover up to the ledge and crawl through the pipe with a green arrow pointing at it.
  
• To access Area 9 (and the good ending) you have to collect ALL upgrades and items (health ups, maps, keys). You don't have to visit the dungeons that only have health and blaster power pickups in them.
  
• You can go back at any point up to the end walking dungeon of Area 8 (the game will tell you it's teh end at that point). Once you defeat the Area 8 boss and enter Area 9 you can no longer go back.
  
• To go back after defeating the Area 7 boss you have to first enter the Area 8 and save there. After you go back the door will now be open. The elevator is no longer usable, you have to use newly opened path on the left.
  
• You can't get all steam achievements on your first run. First you have to beat the game to unlock the additional game modes needed for the achievements.

You can find more info about specific areas, enemies and upgrades on this wiki: https://blastermaster.fandom.com/wiki/Blaster_Master_Zero

These maps were originally posted here[gamefaqs.gamespot.com].