Don't do the Reptite village quests until you've done *everything* else in the game. They're absolutely awful and there's a good chance you'll get tired of the game, quit before you 100% it and end up having done the Reptite quests but not something else far better (like different endings). Speaking from personal experience here!
The monster training is pretty bad too, I thin, but. it's the type of system where time other than what you've specifically spent on it matters, though, so I guess it'd be best to start earlier than later if you know you're going to 100%...
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[NO BARKLEY NO PEACE]
im here to you dark soul with my LIGHT -ertyu