Object - Official Teleporter:
Instead of having to change values and whatnot, I'd make an official object actually dedicated to teleporting, rather than the annoying jump pad crap that goes on today. Also, enemies would be able to travel through portals.
Enemy - The Ghost:
If you have played the DOS game Jetpack you know what I am talking about. The Ghost would be able to pass through any object or wall and would constantly move towards you at a laser drone type of pace. It could get to you know matter what, but its speed would make it easily avoided.
And now that I'm talking about DOS Jetpack, I'll snatch a few more enemies from there.
Enemy - The Marble:
It would look like a regular zap drone but be effected by gravity. If it was set to surface follow it would not be able to float in mid-air, instead it would simply fall off objects in the sky. It would keep rolling until it hit a wall steeper than 45 degrees or got trapped in a 1x1 pit. In combination with the teleporter, this thing would be a new type of dangerous fun.
Enemy - Ninja Star:
It is what it sounds.. Except friction doesn't exist for this enemy. It'd be a ninja star that would continually bounce in 45 degree angles every time it hit a solid object (excluding bounce pads).
Object - Freeze
This object would look exactly like gold but would be silver. When you picked it up it would cause every enemy on the map to freeze for 5 or 10 seconds. This would allow for some crazy race maps and creativity expansions.