You can find all the information you'd need about TADS games here, but the basic explanation is it's a text-based game. Basically, you'll see text descriptions (ie, "You are in a room. There are three doors, facing north, east, and west.") and can give text descriptions (ie, "go north"), in which the game will interact with you (ie, "The door is locked."), in which you can interact back (ie, "look around"), and the game will respond to that (ie, "You see a key in the middle of the room."), and so on (ie, "pick up key"), and you can use it to solve puzzles (because lo, with the key, you can go north!).
The games won't be completely customized, because we can't do one for each character. But there will be several different types depending on if the character is more of a physical fighter, brainiac, normal person, or whatnot. And they'll be semi-customized with name changes and possible dialogue differences (ie, if there's a point where a character sees someone dead and important from their past, Ed (FMA) would probably see Trisha, whereas Harry (Harry Potter) would see either Lily or James).
So how do we know if you've gotten to the end? At the very end, the game will give you a password. You can then send the password to the mod account.
Of course, you don't actually have to do all this (please do tell me if you don't want to or don't have time to), and if you know even a little bit of programming, you should be able to take apart my code and find out the password from that, especially since I gave the main site where you can get the game-writing software and not just the game-playing one, but anyway.
Please either respond to this post or contact Ari (you can find contact info on the comm profile and this mod account profile) once your character is ready to go into the cave.
There should only be one person in there at a time. However, special permission might be granted for other circumstances, for example, if the characters are twins, lovers, etc.