Memorial Buff is a skill used by Light
It seems to be a skill that recreates a buff that Light has used in the past.
When the skill is used, 11 Lucky Coins are automatically flipped which allows Light to enter 'Transcendence' and become Majin Light.
Notes & Trivia
- The exact nature of the skill was never revealed, but it seems like Light is able to use a buff he had previously used in the past. Seeing as Hungry Ghost was killed, Light could not use his Lucky Coins so used the skill to recall the buff he had previously used to turn into Majin Light in the previous PvP Rounds.