The Aqua Crisis

The Aqua Crisis was a destructive event that occurred in the Land of Ooo, in the year 3015, after Finn's constant broken heart, and compassion of being used by too many of the princesses' of Ooo, reaches its peak, eventually causing him to go rogue and submerge most of Ooo, which in turn would be the main event that reawakened Ocara, who had been asleep for the past 1,655 years, since his reconstruction 16 years ago, during Human Finn's creation, which in turn was responsible for merging his age to Ocara, thus eliminating all strands of any human DNA that he possessed within him, making him older then anyone in the apocalypse land of Ooo and Earth, with the exception of Hunson Abaneer, and Prismo.

Finn's destructive ways lasted for an entire week, until the 6th day when he was eventually encountered by Electroga, and nearly killed.

At some point, Finn is later reformed with the help of convincing words from his ex-girlfriend, but is nearly tortured to death by an angry Electronica, who was responsible for unleashing Electroga on him during his fight with Flame Princess, back in the flooded grass lands. He is then rescued by both Flame Princess, and Princess Bubblegum, who was able to escape the dungeon they were in, and enter his chamber with the help of Ice King who had at one point followed them.

Unfortunately Finn is badly injured and left in a temporary coma, where he is then taken back to the Malian Temple, which was known to be a field headquarters and safe haven for the remaining Royals of Ooo, for the Kingdom's Finn had completely destroyed during his rampages, but is soon attacked by Malice and Insurrection, where both he, Flame Princess and Ice King are captured.

While trapped in the Raliorvo Ruins, Finn loses his power along with Ice King, and Flame Princess, but are able to escape, while at the same time learning about the Insurrection and the propaganda tool that is being used to turn the world against Finn. Unfortunately it was discovered that Finn's powers have been reformed by an unknown source and Finn soon would end up in a one on one battle with his own self. Despite receiving multiple injuries, Finn eventually destroys his dark half and is able to regain it again, but is heavily wounded and separated from the other during this fight He then retreats down the forest to the fields of Plemsworth, where Marceline soon caught up and led him to the ruins of an unidentified city, in order to spend the night.

It was from here that Finn would discover his true past, and his true age, revealing by the end of the crisis Finn was proven to be over 19,996,982 years old, stated by chapter 15.