9 Secret Levels You Missed In This Decade's Biggest Video Games

6. True Final Boss & Ending - Sonic Mania

Defeated Robotnik and seen the credits? You're not done.

As if Sonic Mania couldn't be any more perfect, there's an additional secret boss to seek out. Triggered by first finding every last one of the Chaos Emeralds (themselves tucked away inside the large golden rings you can see within each zone), you then need to fight Robotnik again.

During the battle, transform into Super Sonic (done by having 50 regular rings and then pressing Jump while in mid-air), and defeat Robotnik whilst in this powered up form.

All this will see the Phantom King appear, being the true final boss of the game. Defeating him gives you a strangely empty-feeling cutscene though, as Sonic gets whisked off through a dimensional portal, only to later end up - thanks to Sonic Forces - battling another version of Robotnik/Eggman all over again.

But hey, at least you've now 100%'d the best Sonic game of all time.