GS:tLA - Sentinel - Total Pwnage

After realizing this boss is weak to Earth and the fact that Charon can be obtained prior to this battle. Just get Serac from the corridor to complete the 72 Djinn collection and visit Anemos Inner Sanctum for the Charon Tablet. Then return here to fight the boss for the Catastrophe Tablet.
Because Sentinel is relatively slow (AGL ~190) you can easily outrun him even with all of your Djinn on standby as demonstrated. Just get 16 Venus Djinn on standby and some more to summon 2x Charon + 2x Eclipse.
After doing so you'll deal more than 10000 damage in a single turn and kill Sentinel with no effort. This is just getting pathetically easy here. :P

[@dcinmich]

Wow, it worked! Thanks Zuq :)