Hooks

I've been dreaming about adding a new tool recently: a grappling hook. I propose introducing a new tool—a grappling hook—as well as a special block to which it can attach. This item would be very useful for moving around in small spaces (like your base). The grappling hook would only attach to specific blocks and nothing else, meaning players would need to place special blocks in advance in the locations they want to attach to.
I think this innovation is quite balanced. It could be a very enjoyable gameplay mechanic, and I'm sure a lot of players would enjoy it.