You will see the Ultra Energy Core feature when you reach the 192nd level.

To get the Ultra Energy Core, you must beat 10 levels or rounds.

You will double the effect of the Energy Core when you activate the Ultra Energy Core.

As long as you don't fail a level, Ultra Energy Core will stay active.

When you fail in a level, the Ultra Energy Core will reset. You need to start over and beat 10 levels or rounds to activate the Ultra Energy Core again.