Here's an awesome bit of insight into the original NES days. Kenji Sada, the original artist on Blaster Master, has put together a video showcasing how he created the in-game art for Sophia, the tank from the series. Sada put together a special video to show how he did this, and he used the exact same tools that he did back in the day.
This video is only possible because someone archived and dumped the development tools Sunsoft used on the NES. Sada was able to grab these and jump right back in to show his original process.