I'm still trucking along at Eternal Poison. Farther than I ever got ten years ago when I first bought it, but god fucking damn is this a difficult strat rpg. You have a few complicated factors... first of all, you gotta win, obviously. Oftentimes within a set amount of turns, which okay, that's typical. Coupled with attempting to get a treasure chest or two if you're a completionist like myself, and the biggest general bitch of all, you have to overkill your enemies by often 100+ HP, sometimes 300 or more, in order to capture them for completing what's essentially a pokedex.
Oh yeah, and the main bosses can only be destroyed/ captured with specific conditions like 'summon a monster you should have caught four stages ago and use it'. You can't travel backwards. Game's broken as fuck as far as accesibility, and not just for shit like that, but damned if it doesn't keep me coming back every few years. Just a really cool mixing pot of concepts.