Mega Octus

The Mega Octus is a boss that appears in Sonic Mania. It is a giant octopus-based submarine that ambushed Sonic and his friends in the Oil Ocean Zone Act 2. It's the second boss of this zone, and the 18th overall boss of the whole game.

Guide
Dr. Eggman pilots a large octopus-shape submarine for this encounter. When player reach the boss-fight area, two tentacles will wrap around the left two platforms, and then submerge them, meanwhile break the two bridges between the three platforms.

After that, Mega Octus shows up from the oil, and Dr.Eggman opens the top-side trap-door to check the outside situation. A little bit sooner, he gets back inside, and Mega Octus submerges into the oil again.

During Mega Octus's twice show-ups, the two missing platforms will rise up, giving the player more places to stay. And Dr.Eggman will attack the player using the same tactics as the original Oil Ocean Zone boss: Submarine Eggman II. He may first deploys a snake-like sting that flies at the player, and the player should avoid only the pointed tip. But this part may also be skipped. Next, a laser cannon will always show up, fire the player three times at random heights. If a laser is fired at platform height, it will temporarily ignite every passing platform, force the player to jump over the fire or jump into the oil.

When the laser cannon are leaving, two tentacles will submerge two of the three available platforms again, forcing the character to jump to the third platform or descend into the oil. Meanwhile, bullet shooter tentacles (from the Heat Arms miniboss from Lava Reef Zone from Sonic & Knuckles) will rise up between the two missing platforms, then Mega Octus will too.

The player can only hurt Mega Octus in this period, but he/she also needs to dodge the tentacles' bullets, or use an elemental shield to simply block them. Each tentacles shoot three times in this specific period. And if any rings fall into the oil when player gets hurt, they will disappear and cannot be picked up again, forcing the player to pick rings back quickly to avoid losing all rings and dying easily.

If Mega Octus is not defeated after the tentacles shoot three times, it will disappear again, also will all the tentacles. After that, the missing platforms come back again, and the player should once more be ready for the snake-like sting and the laser cannon.

Hit Mega Octus submarine eight times to end the battle. As with the Heat Arms fight, destroying the bullet shooter tentacles can be done by four-times-hit each, but does not contribute to the victory condition of the battle. However, destorying the shooter tentacles does make this fight easier, because the player can hit Mega Octus safely from now on.

Trivia

 * There're some issues in this boss fight that may cause the player to die immediately regardless of the ring amount:
 * If the player choose to stay on the platform when a tentacle is trying to submerge it, usually the player will be slow down by the oil and stay safe. But there's also a chance that the player will ignore the oil and continue falling, leading to a immediate death by falling off the screen. It has been considered as a bug.
 * If the player choose to hide under the platform to avoid lasers, he/she should get out quickly, or else when a tentacle tries to submerge the platform, the player will finally be crushed to death. Besides, the shooter tentacles may block or even hurt the player when he/she wants to escape out, and force he/she to accept the fate.