Platform: Windows
ISP: Comcast
Type of Internet Connection: Cable
Internet Connection Speed: 90Mbps
Date & Time: March 16th, 2016 17:10 EST
Frequency: Twice
Character Name: Rwolf
Race: HumeM
World: Bismarck
Main Job: Black Mage, Lv.99
Support Job: Red Mage
Area and Coordinates: Mog Garden
Party or Solo: Solo
NPC Name: Chacharoon
Monster Name: none
Steps:
  1. Obtain Rank 6 Monster Rearing
  2. Obtain Snoll memento Permanent Key Item
  3. Speak to Chacharoon and Discuss Cheer Effect
  4. Select Rank 6 monsters.
  5. Obtain Snoll memento cheer.
  6. Observe MP only raises by 20.

Description of effect from Chacharoon says that it increases MP by 16%. It could be that 20 MP is the cap but this seems questionable for a rank 6 memento.