If you're avoiding spoilers, don't read any further.
Before the credits roll, we rejoin the villainous Dr. Robotnik (Jim Carrey) on the mushroom planet where he ended up after the movie's final battle (possibly a reference Sonic the Hedgehog 3's Mushroom Hill Zone). He's looking a bit of a mess after 87 days trapped on the desolate world.
"My grasp on sanity remains absolute!" Robotnik says, in a tone that suggests otherwise.
He's also talking to a rock with his henchman's face painted on -- a literal Agent Stone -- and shaving his head.
"I'll be home by Christmas," he exclaims.
Watch this: Sonic the Hedgehog: Jim Carrey is jealous of Dr. Robotnik's 'ridiculous' moustache
What it means
Robotnik will return, and he'll be rocking his bald-with-wide-moustache classic video game look (a shot inexplicably spoiled by the first trailer last April).
Midway through the credits, a giant ring portal opens up on a cliff outside Green Hills, Montana, bringing to Earth an anthropomorphic twin-tailed fox: Sonic's longtime video game sidekick Tails.
"I've found him! I hope I'm not too late," says Tails, before using his rotating tails to fly towards the town.
What it means
We don't know what he's talking about, but it's possible Tails knows about some otherworldly threat to Sonic. After all, he was hiding on Earth to escape unnamed bad guys who wanted to use his speed powers, and it's likely his very public battle with Robotnik alerted them to his location.
Tails (real name Miles Prower, a lame pun) became a video game icon after appearing in 1992's Sonic the Hedgehog 2. He's been Sonic's sidekick ever since, and his humility stands in contrast to Sonic's cockiness.
There's nothing after the credits -- I guess they're saving Knuckles the Echidna for the end of the sequel, or he'll be the threat coming after Sonic -- so you can go home or turn off the movie after seeing Tails.
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