What would be the optimum build for end game bonus dungeons and trials? I heard Courage build for Hero is the best with Whip for Jessica?
I usually go for high Courage for the Main Hero when I want to get through the post game stuff. As for weapons and such, you should look at each skill list and see what you like. I would recommend at least getting the Hero skills in Spear, Courage, and Sword to get:
Spear > Lightning Thrust for Metal Slime hunting since they are hard to hit and will give you massive experience, lower miss rate than other critical attacks
Sword > Dragon Slash for post game bosses
Courage > 1/2 MP Cost since your Hero is a great spell caster and healer, especially when you get Omniheal (fully heals all allies)
If you want more stuff to think about, think of Fisticuffs. It's a skill tree most people don't think about since it's not as cool as holding an actual weapon, but some of the skills are worth it, especially in post game. For example, Defending Champion is useful since it reduces damage by 90% when you use that skill for that turn. It's useful for certain bosses in at the end game.
If you want to focus on swords, then get up to at least Falcon Slash. If you have Angelo specialize in swords then get him Falcon Slash, too, then you have two massive damage dealers, especially when you use the tension/psyche system.
The rest is just experimentation. You can't really mess up that bad, but I found those skills and abilities for the Main Character to be useful.
Just noticed your question regarding Jessica:
I think the best build I've used for Jessica is a mix between Staff, Sex Appeal and Staff. Basically nearly max out Staff and Sex Appeal while only spending 23 points to get Twin Dragon Lash in Whips. The Whip is useful for post game, especially with the Twin Dragon Lash for post game. Staff just has too many benefits to ignore, especially for Caduceus (basically Midheal for 0 MP) and Kazing (revive all at max health). Sex appeal is usual for random battles, but Hustle Dance was super useful since it heals like 80-100 HP for everyone for 0 MP, but best part is that it works with the Psyche Up/Tension system.
Last bit of suggestion is Fisticuff for Jessica as well if you don't like the abilities above. At some point, like 52 or something skills in Fisticuffs, Jessica gets Evasion Up or something that increases her evasion a lot when she does not have a weapon equipped. This helps her survive in post game where defense isn't as useful as just dodging attacks. Since her defense will always be lower than the rest of the party, this was useful.
Anyways, just food for thought. If anyone else has suggestions, then please feel free to add to them. These worked for me, but perhaps aren't the best builds.
It's been noted earlier in the thread, but I should probably reiterate: twin dragon lash has received a sizable nerf in the 3DS version. It went from 1.5x damage per strike to 0.9x damage per strike, which makes it weaker than regular attacks on multiple targets. Oomph was buffed to be 2x damage, but it only affects the first hit of multi-strike attacks. This means twin dragon lash is still okay against bosses, but not the powerhouse it once was. On the other hand, Jessica's 100 point knife skill sudden death was buffed immensely, to 1.8x damage (which makes it 3.6x damage with oomph). So that's something to consider.
Ok, I didn't know this...so...ignore my suggestion with whips. Maybe don't focus on Whips until Twin Dragon Lash... I still think Whips are useful for random encounters. Thanks Aeana. I'll focus on Knives and see how useful it is in this version.