One per game is tough.
1. Green Dragon. While Dragonlord is the obvious choice, the Green Dragon at mid-game sticks out as a miniboss. It's something different. It's tough. And you know something is there past it.
2. Malroth
3. Zoma - Wait, the game's not over?
4. Balzack (original) - You know this guy is bad news in the first go round, but once you're at this point in chapter 5, you know it gets much tougher from here on out.
5. (remake) - Ladja - Gema in the original, but the update made this guy nastier as an individual.
6. Mudo. One of the toughest bosses out of all the DQ games.
7. Tough picks here. Hellcloud's my achilles heel and sticks out on pure combat. Gracos, Deathpal, that boss in Dharma, not to mention Demon Lord and God.
8. Marcello. You just knew you're going to fight him at some point.
Currently playing - No time for games right now. Next one - DQVI for DS
RPG/Adventure Games/GTA style Action games beaten (not necessarily 100% completed)
DW/DQ 1-8, DQ4DS, FF 1-XII (outside of III, XI, X-2), FFIV DS, Arcanum, Earthbound, Fallout II, Ultima IV, VII, Serpent Isle, IX, Gabriel Knight I-III, Police Quest I-IV, Kings Quest V, Leisure Suit Larry I-III, Culpa Inata, Indigo Prophecy, True Crime, GTA Vice City, GTA San Andreas, True Crime:Streets of LA, all the CSI games, Suikoden I-V, Suikoden Tactics, Illusion of Gaia, Zelda I-III, Crystalis, Might and Magic VII, VIII (Finished, but hollow victory, not nearly completed, game sucked anyway), Suikoden, Under a Killing Moon, Overseer, Pandora Directive, Law and Order. Criminal Intent, Knights of the Old Republic I & II, The Godfather, Persona 3, Persona 4, The Longest Journey. Radiata Stories, Persona 3/4, Ace Attorney,
Games almost beaten - GTAIII, Scarface, Might and Magic VI, Dragon Quest IX,
Played haven't beaten - Fallout I, Ultima III, V, VI, VIII, Phantasy Star III, Law and Order Criminal Intent, Leisure Suit Larry V, The new Larry game for PS2 that sucks, Baldur's Gate: Dark Alliance, Might and Magic IX, Dark Cloud, Sherlock Holmes: The Awakening, FFIII DS, Zelda: Phantom Hourglass, FF Tactics Advance (DS/GBA), Dreamfall, Chrono Cross