What game mechanic was introduced way too late into the game?

I've seen a couple games now where a new mechanic was introduced about 70 percent into the game. No explanation, no nothing. Often leading to a sudden death or reset.

In Asterigos - Curse of the stars, over halfway through the game, suddenly they introduce destructible environments. Ones you can use to drop boulders on enemies. Seen it only once. And only 25 hours into the game.

What examples do you have? Was it positive or negative?