I am constructing a barebones engine for my game, and because of its structure, it it very easy to create and implement new features, even after the game has been finalized and published. The specifics of doing this isn't too hard, but what I'm struggling with is the best way to present it.

My game is a 2D puzzle/horror game that has a large focus on story. As such, there is a natural progression of mechanics and difficulty; it may start with a simple button and door, and more to remote control puzzles, and finally work with challenging momentum physics puzzles that require more reaction time. Therefore, there may be mechanics that are slowly introduced and fit into the story.

However, what do I do after the game is done? Currently, I plan on improving replay value of my game by offering later updates in the form of a sub-game I'm currently calling "The Tower." In it, the player is subjected to a supply of new maps at random and with each update, more maps will be added, turning it into a game of "how many can you solve/survive?"

But let's say that I end up introducing a mechanic that's entirely foreign to the main story game. After playing the story, the player may be familiar with traps, buttons, doors, toggle switches, spikes, spawners, teleporters, and enemies. But what if when I make an update to expand on what can be done ingame, I create a new game mechanic? For the sake of explanation, let's say it's a window, which can only be smashed with an object moving fast enough. The player would have no knowledge of this; it may even seem like scenery for some, and they may never make the connection that it's an important mechanic.

In the story it could have time to be introduced, but if this mechanic is introduced after the story has been finalized, then it would make no sense to go back and change the story. And because changing the story is out of the question, that would leave just simply slapping it into "The Tower" sub-game, where it would be randomly show up without explanation or exposition.

So what I'm asking is: In a game where the story has been finalized, but the potential to add more content exists, what are ways to properly introduce new mechanics without simply telling them every time? What are ways to add new mechanics and puzzles into a story-driven puzzle game?

Thanks for taking your time to read this :)