Specifiable end

This is less of a full game idea and more of game mechanic idea. In multiplayer mode for any game, there is usually a definite objective such as getting to somewhere faster than everyone else, collecting the most of something or doing a specific task the most times out of all the players. For the latter two it will usually be coupled with a time limit to ensure that rounds are not too long or too short if the players are inexperienced or expert respectively.

This time limit, while sometimes customisable before the round begins, is a constant, allowing know when the round will end. If the players could end the game at whatever time they wanted (with a majority voting system) it could add a whole new dynamic to the gameplay. But rather than the game ending as soon as the majority indicates that they want to end, the game plays on for a certain amount of time afterwards. For instance, if the goal of the game was to collect coins spread out around the map, people could pretend to be bad at collecting coins, offer to end the game then quickly collect a lot before the time runs out, while the opposition is relaxing thinking they have it in the bag. This would almost allow for poker-like tactics of bluffing and double bluffing. This would be coupled with the score being hidden during the final minutes of the game, so as to not alert the opposing side to what you are doing.

Déjà Vu

Picture this: you're playing a platformer game and you are walking along. You see a red button so you step on it, thinking that it will aid you in completing the level somehow. Suddenly a spike falls down from the sky. You 'die' and have to start the level again, but now you know not to step on the red button.

A lot of games require you to restart the level should you die. However the twist in this game is that restarting is part of the game, instead of a punishment for doing badly.

Each level would have a time limit, and if you didn't complete the level in under the time limit, it would restart, the same as if you 'died'. This means that if there was more than one way to complete the level, you may have to find the faster way in order to advance to the next level.

The real trick to this game would come after a few levels with just these mechanics. Probably in level 3 or 4, you would find a level that changes everything. There are two ways to go, one to a key and one to a door (and the end of the level). No matter how fast you run, if you go get the key, you cannot make it to the door in time. But if you do not get they key, you cannot unlock the door. There is a trapdoor that leads from the area the key is in to the area the door is in, but the lever for the trapdoor is down below, near the door.

If you pull the lever, the trap door only stays open for 3 seconds. And there is no way to jump up through the trapdoor. You may notice, though, that the lever is glowing blue.

Before you have a chance to work out what it means, the timer goes up once again and you restart. You walk down to the lever again and notice that it moves itself, right at the same moment you pulled it last time. You wait for the timer to go up, and then you walk back to the lever again, but this time you pull it as soon as you get there. You restart, climb up the ladder and get the key, walk through the trapdoor that seemingly opens itself, and simply walk through the door.

To cut a long story short, if you interact with a glowing blue object, then that interaction stays the next time you do the level.

Consequences

Okay, it's only the second idea and I'm already resorting to thinking up platformer games. I'm not really out of ideas, I just think that platformers are such a great game type because most people have played one before, and it's so simple to learn how to play even if they have never played before. Essentially then, platformer games are a blank canvas on which you can put new, unique features and mechanics.

So my idea: A basic puzzle platformer, where you have to collect coins and keys unlock doors etcetera. But the twist is that wherever you walk you leave a faint ghost-like trail behind you. The trail does nothing except look cool - until you die. When you die you have restart the level, but the trail turns solid. Every time you die the last trail you created disappears, in order to prevent the level becoming a tangled mess. There could be a 'self-destruct' button so that you can arbitrarily decide when to create the solid trail, and completely restart the level if you need to (by self-destructing at the very beginning there would be no solid trail next time, because you hadn't moved to create a ghost trail yet)

So, this trail system is great an all, but how exactly does it make the game more fun, difficult or interesting?

Well think about this situation: there is a bottomless pit of brimstone and hellfire and you just can't quite jump all the way across. By jumping in once, your trail creates a bridge that goes half way across the pit. You are then able to walk on this bridge and jump off it to the other side of the bridge.

My friend No-Eyed Pete does a better job of explaining below:

Another challenge could involve a platform high in the air that you need to get to, but you just can't jump high enough. By jumping up and then self-destructing, you have created a nice step on which you can jump to get the rest of the way up to the platform.