I have been getting some what are new to me PS1 games and even though what are listed below are excellent games the final bosses are incredibly stupid.
Syphon Filter 2
Is without a doubt is the hardest, yet very fun and excellent game I ever played but has the stupidest final boss in video game history. Since it is invincible you have to get it to walk in to the rear blade of a helicopter.
When you finally make it to the final boss level, you figure at first it's going to be a hard one to beat especially when it starts throwing fireballs at you and you can't do anything about at first until you unlock a platform that puts you on the same level as it. That is where the game turns stupid. Instead of being like ever !@#**&$ boss in the game, it runs away and it turns out the only way to beat it is chase after it and knock it off of it's feet.