Beat
in Chrono Cross. Damn, an actual challenging boss! Not exactly superboss tier in terms of sheer difficulty, but rather design. He would always respond to offensive elements by using a preset opposite element against the last member to hit him - so not necessarily the one who used the element. Blue and red were "safe" in that he'd only use debuffs in response, while white elements (his weakness) would be responded to with a 'fuck you' tier black move which would certainly one shot anyone. The trick was to equip black draining armor and bait those attacks, which required some preplanning of attacks as bad luck with hits or simply attacking at every opportunity might leave the party at low stamina and with no one able to cast any appropriate element before the boss' turn, leading him to autoattack if lucky, or use an element to one shot someone - and I only had one revive to spare. All of this is made more difficult to predict by the game's omission of a turn order indicator - you have to gauge by feel how many attacks you can get in before the boss' turn. It felt like a dance which is also the impression I've gotten from difficulty bosses in other JRPGs.
The reward was a damn fine sword which may even be the protag's ultimate weapon, not sure yet.
Missing out on the element absorbing armor is also easy to do as it is pillaged from the dragon bosses which one might not think to attempt. Those dragons were also a small bump in difficulty - in that I actually had to plan out what elements I brought and on whom. I think they were a bit cautious with boss HP - any boss I've fought so far could have had their HP increased by 25% and that would have been more than fine.