The Hardest Boss Ever

The Last True Boss from the Japanese arcade game Mushihimesama Futari by the developer Cave. The final boss from the original Mushihimesama on the "Ultra" difficulty mode was widely considered to be the hardest ever before this sequal came out. Not only is the screen completely and utterly drenched in overlapping bullet patterns, but the player is subjected to the unusual cruelty of completely draining the bosses health bar only to see it fill right back up and an even nastier form reappear. I can't even imagine what people playing this in the arcades felt like when they finally destroyed the boss after 3 minutes of pure torture, only too see it come cackling back with a mind boggling array of new, seemingly undodgeable bullet patterns. The player's only consolation is a hit box the size of a single pixel: the pilot's canopy.