Hey all, I'm struggling with an idea for the theme so I'm making a platformer and was wondering what you all would deem essential to the gameplay?

So far I'm working on art at the moment so no game or levels have been designed yet. 

I got so far:

• a basic player sprite
• collectible small and big coins
• floor palette changed tilesets x3
• animated water/lava/void,
• two possible mobs
• end of level and checkpoint flags
• a couple of obstacles.
• basic bitmap font.

After starting to list these I did think about possibly moving platforms so I will do art for them in a bit.

Are there any other things that could be in a platformer?