[Buzzzy]

Idea-wise and if I can permit myself the suggestion, I've personally be fond of exploration side-scroller such as Metroid or the NES Faxanadu game(even if some people considered it a bit poor due to poor translation). Perhaps something akin to this could be done? Might also permit for a broader universe, if taking the faxanadu-like approach where you even had towns with villagers and so on(one of the interesting part of the setting was the "world tree" that basically was the game world, the town basically built inside the tree's roots/trunk/branches).

In such a setting, perhaps different forms could be used to access different zones like in the two example games where "newest tool of the moment" did the job. Additionally, it might be able to take a small RPG/adventure turn with towns were you could buy items for recovery and such(as was the case in faxanadu).

Of course, this might make for a slightly more complex game than first intended.