Toughest boss I'm ever going to know comes from Romancing SaGa 2 for the SNES. I dare any of you to beat this boss legitly, that is, without using the most powerful water spell that cancel's the enemies attack that round. Heres a little bit about how the boss works:
"This is a multi-stage battle. Every 6000 HP in damage that you deal to the
boss, the body of another Hero sprouts out of it. It starts with Rocbouquet
at the beginning of battle, then Subier (blue guy with single horn in forehead),
then Noel, and then randomly with the other four Heroes. Now, this is very
important: the final boss has available every technique, spell, and signature
move belonging to those Heroes currently visible. So, at the beginning with
Rocbouquet, the final boss can use Temptation, an electrical attack, Siphon,
and weak epee attacks. As soon as Subier pops out, however, the final boss
ALSO has Maelstrom, water spells, and spear attacks. For every Hero visible,
that's one attack the final boss has, every turn, choosing from any attacks
belonging to those Heroes. So by the end of this, the final boss will be
throwing seven attacks at you EVERY ROUND, with everything ranging from weak
stabbing attacks to Maelstrom and Psycho Bind. Scared yet?
As I mentioned, each "stage" of this battle has 6,000 HP before the next form
will open up. Any damage done over that 6,000 is wasted, because the HP resets
upon form change (so if you hit the boss with a 7000 damage technique, that's
1000 damage wasted). After all seven Heroes become available, the HP resets to
over 65,000. So, in total, the final boss has around 100,000 HP."
So, I guess you can be considered an RPG god if you beat this game the "legit" way. I however, pussied out and went with the spell Quicktime, so I didn't have to endure THAT many attacks.
