Well since you broached the subject....
I've been thinking a lot about that as I work. So far I'm just designing with a rough idea of how I want people to progress. Once I get to the interior, I will have to go through and methodically figure out how that's going to work.
But this is what I know. I want to keep people's options fairly simple, and close to the spirit of Castlevania. I.e., walls stop you, you don't go free scaling terrain or barriers on a whim. Many doors will be locked with super special keys, ect....
Were I to run this in D&D, I'd allow for far more flexibility. But being that I want to run this as a forum game, the format needs to be relatively simple. I want to allow people to do stuff like climbing and make some more free form choices....but with some blanket restrictions. Like 10 feet is too high for anyone to scale. Doors locked with special keys can't be smashed or picked open. Even though there will be hundreds of windows, there will be no smashing through them so you can just take a short cut.
For anything that even remotely resembles platforming, it's going to be abstracted and the areas are going to be designed especially for it. There will be no things like grappling hooks or bat form to go flying around as you please. That would totally break what I'm trying to accomplish, and it pretty much flies in the face of the spirit of Castlevania to begin with.
Depending on how Round 1 of this insanity shakes out, I may revise my rules. But I'm going to start out being fairly restrictive, and any circumvention of the terrain (jumping, climbing walls, ect....) will come down to dice rolls on whether you succeed or fail, and failure will likely be fatal. So on the one hand, I don't want people trying to climb short barrier walls. But on the other, I want to leave the possibility for that in certain places, balanced by the risk that you're going to die trying it.