I know it is a straight-forward game, but is there a guide anywhere that has possible secret areas and ways to get to/unlock them? or a guide period?
I don't think there are any secret areas... *looks through the editor*
though there was this hidden skill if you hit z on this spot (its the map between the hub and the maze) outside the lava cave
you can take on the final boss at any point after you get the arrows but i recommend doing all the other bosses first.
as long as you learn the plant monsters weaknesses you can grind for permanent stat boosting items too.