Can i add more cool mechanics in the game like cheats or any new combos as well
and can i Add non pixelated sprites

and can i modify the ui

oh and can i add a start screen that moves to the main menu with animations

and if so how would i go about doing that

and one more thing when or have you already added a map editor
and is there powerups of any sorts?

You can modify any part of the game and do (almost) anything that GameMaker supports.