How many different mechanics do you like in a game?

I am currently in the process of creating a 2D statless action RPG. The game engine I have created is very versatile, it currently contains 2d physics, lighting and particle effects, quests, weapon upgrades, both for sidescrolling and top down action.

Just to see what the engine could do, I have created a lot of different avatars and control schemes, for example: A sidescrolling vehicle simulation using accelerating/braking, a top down tank simulation, a spaceship using newtonian controls, war planes using direct controls, a platformer with double jumps and wall jumps... the list continues.

During development I realized that this allowed for a lot of good and varied storytelling, and dreamed up a lot of scenarios where you first had to invade a planet, drop a space buggy and drive over dangerous terrain, invade a beach with a top down view and explore a cavern using the side scrolling view.

So - here is the question: How many mechanics do you think is viable to put into the same game? GTA V does it well, and so do some other games, but I am also targeting mobile and with just touch controls you are a lot more limited. Would you find it annoying/confusing having to switch between different control schemes during the course of a mobile game?

And - would you play a game like this on mobile, or should I just skip that platform for now and create the game for keyboard/mouse/controller input?

The Fewer the Better......

What you want to do is have one mechanic and ten million different scenarios you can make for it. If you can do more than do it one mechanic at a time.

However many or as less, as long as they're well utilized. Dishonored does it pretty well.

Would one mechanic per level be okay then?