Funny thing, I was just thinking about this. Rewinding all the way back to the PS1; more specifically: Crash Bash. That fucking tank boss: Big Bad Fox. First off, it spams 3 spike balls at a time at you. Your tank is so slow there's no way to dodge, and the enemy shots bounce off everything. After that, it spams 4 energy balls at a time at you. Next, it shoots lasers that drop you by 75% of your health. What's more, it can destroy healing items, and you have an obscenely slow rate of fire. Finally, after all that, you reach a checkpoint. Then you have to kill a pair of enemies in tanks. Fortunately, you get a better gun than them. Most of the tank battles in that game were a huge clusterfuck, but I'm still glad I found it at the pawn shop.
Another notorious boss from the PS1 was Anubis Rex, from Pac-man World. He bombarded you with meteors, tornadoes and ancient egyptian laser beams. And more surface area led to an instant death than didn't.
Another enemy that was just pure evil, was this one super Yux in the X-Naut fortress in Paper Mario 2. If you didn't kill it in 3 turns, it could not only become invincible, but continually stun you with no way to escape.