Despite the fact that there are a thousand of these threads I'll post anyway.
-Land form : A basic field item (like respawn area) with a number of properties like height, dropoff, smoothness and things like that.
-Object Merge : The ability to place objects inside of each other, this would be toggled (without having to make things not appear at the beginning of the round and allot of guesswork).
-Floating Objects : The ability to drop objects in mid air and them not fall, this would be toggled.
-More Basic Geometry : Simple things like Glass or City Building Wall 01 that you could change the dimensions of and essentially construct things as complex as the New Mombasa metropolis in ODST.
-Basic Physics Changes : Similar to the physics changes allowed with the Halo custom edition like lower gravity and things like that.
-Weather: Making the level day, night, raining, snowing, sunny whatever.
There are more but I can't think of them right now.