level off vs level up

level off

verb
  • to get to a stable level; to cease climbing, descending, or oscillating 

level up

verb
  • To raise to the same level or status; to improve so as to make as good as others. 

  • To progress to the next level of player character stats and abilities, often by acquiring experience points in role-playing games. 

How often have the words level off and level up occurred in a corpus of books? (source: Google Ngram Viewer )