I love your LO theme! Such a good game.

I think I'm only missing 20G, since I never downloaded the extra DLC. That 20G is the achievement for getting all of the treasure chests. I missed one, I'm pretty sure I know where it is, but after combing the world for ONE missing Seed (that I finally got, after hours and hours of searching) I haven't been in the mood to go back and seek it out.

For mastering immortal skills I just sat down and did it at some point. I got all of the Seeds so I could get all of the accessories, was very careful to get all of the treasure chests (though, apparently not careful enough!), just kinda went all out until I had every single accessory, and then I used a party of 4 immortals and one mortal that they were learning skills off of. I swapped around their accessories as they completed skills, and having Sed's "Double SP" on helped a lot. There's one area in particular (I don't remember whether the story sends you there or if you have to seek it out yourself) behind Gongora's mansion (once you're inside, go to the left and leave the building, the entrance is in that garden). You use Tolten to break the seal and then have access to an area where every encounter will pit you against 5 or so monsters of the same kind. If your characters are equipped well (especially if they have the right rings on for extra damage!) you can take each monster out in one shot. Each fight gives you 10 SP (I think it's 10 SP WITH the "Double SP" skill, but I'm not sure, it could potentially be more). Just fighting like crazy down there for 10 SP every easy battle made it relatively easy to get everything maxed. For getting all of the accessories, just be really careful about Seeds, chests, and stealing from bosses. Looking for extra quests helps too.

Sorry that was so long, hope it helps a little. LO is an amazing game.