These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Game Breaker: Heracles in the second game. Though he can't cast magic, he's the strongest character in the game in nearly all stats. Although it makes sense, given that you did beat the first game with him and all.
Genius Bonus: In the DS game, the herb that cures Poison is called Mithridate. This is named after Mithridates VI of Pontus, who was said to have built up an immunity to poisons.
It's Easy, so It Sucks: This is definitely not a series you play for its challenging battles. The games before the DS entry are damn hard though. Several enemies in the second can DESTROY any of your equipped items, and by the time you start hunting the Taphoi in the DS game, the difficulty hikes itself up a notch or two.
That One Boss: The Sphinx in the DS Game. It took this troper about 10 times just to get close to killing it. CURSE YOU COPYING!!!!
It's actually pretty easy. Spend a turn or two chanting for the mages, and using focus for the melee characters, using only healing ITEMS if you need to, and you can probably take it down in one turn of attacks. Heck, just chanting and focusing for one turn first I got it down to half hp right away. And I was under leveled.
I didn't have much trouble with the Sphinx, and I didn't go out of my way to do anything special, either. I focused almost entirely on Physical attacks, and the few times I did use magic (Sthen/De'Gird), it missed on its revenge cast.
I'd say this boss pretty much qualifies. Though, you can figure out you're supposed to use that one ice spell, what player playing the game for the 1st time figure that out? Not to mention your party isn't even level 10, and Axios doesn't have a lot of MP. Overkill does restore all of it, but again, the new players? If that doesn't tip you off, it has way too powerful attacks for that point of the game...
I didn't seem to have much trouble with it. If you need a hint, equipping the Bomb item on Leucos, and then Byrn-spamming with the main character on the boss while it's Attuned REALLY speeds up this fight. And if you run low on MP, pretty sure you have Boon by that point... if not, hit the afterimage copy for an Overkill recharge. Easy.