Dream Devourer is a boss that appears in Darkness At The End Of Time in Chrono Trigger (DS). It is an early form of the Time Devourer. A Magus from the future (possibly an alternate one) and three members of Crono's team face it. Neither Magus nor the player's party are able to kill it or free Schala, however. But even though they can't kill it, they have the hardest battle in the game, rivaling the previous superboss, Spekkio's Final Form. A team of lvl 60+ characters should be sufficient to beat it, however. To obtain access to him, you must have beaten all 3 dimensional vortexes. Beat the creature to win the Dreamseeker.
The battle with the Dream Devourer happens in two phases. In the first phase, it will counter all physical attacks with Mana Reaper, which depletes your MP. Use strong magical attacks like Luminaire, Flare, and Electrocute here. Be sure to get through this phase as quickly as possible since the Dream Devourer has the ability to void status immunity. When you see it do an action that looks like Lavos Core raising its defense, it has started the second phase. Now it absorbs all elements and counters every attack with Chaos Zone, which inflicts confuse. Use non-magical techs like Cleave, Frenzy, and Triple Kick. Everyone should have status-immunity equipment to avoid being affected by Chaos Zone. If you have been attacked by curse and have managed to make it to phase two, you might want to restart the battle. Keep everyone's HP high; Chaos Zone can easily deal two or three hundred damage to all party members.
One good party is Crono, Ayla or Robo, and Frog. Ayla should have her Bronze Fist, or Robo's Apocalypse Arm and the Dragon's Tear. In the first phase, Crono uses Luminaire, Ayla/Robo does a standard attack, and Frog heals. In the second phase, Crono uses Frenzy, Ayla/Robo still attacks, and Frog heals or attacks. If the situation is dire, use Slurp Kiss to completely heal everyone and restore status.
Since the Dream Devourer has 32000 HP, which is close to the signed 16-bit integer limit, it is actually possible to defeat it by healing it. By using powerful magic that it absorbs during its second phase, it can be (temporarily) healed past 32767 HP, which overflows the counter and makes its HP go negative.