After having played this game several times over the years with a lot of serious attempts, I finally beat it today, 14 years later. Full strength, health, then spirit. All points into smaller orbs, no points into explosion. Lost only one life.
Isn't it weird how stage 16 and 17 are the same, then you get the health orb upgrade after a regular stage 20 (the notification screen flashed, i didnt have time to read it), then the final boss is at 21?